Fix several leaks in tests

All of these are specific to tests, not the library code.

For the moment, `protocol_xfer` still leaks connections (and anything they hold on to) because it is very difficult to disentangle them from the connection manager in the partially implemented state they are in.

This fixes leaks of options in the account option test (these two leaks occur for every test since they all leak the option):
```
61 (48 direct, 13 indirect) bytes in 1 blocks are definitely lost in loss record 133 of 276
at 0x4848464: calloc (vg_replace_malloc.c:1340)
by 0x49F75F0: g_malloc0 (gmem.c:163)
by 0x48C3B2E: purple_account_option_new (purpleaccountoption.c:78)
by 0x4014AF: test_purple_account_option_copy_int (test_account_option.c:67)
by 0x4A1CC7D: UnknownInlinedFun (gtestutils.c:2933)
by 0x4A1CC7D: g_test_run_suite_internal (gtestutils.c:3021)
by 0x4A1C9E4: g_test_run_suite_internal (gtestutils.c:3038)
by 0x4A1C9E4: g_test_run_suite_internal (gtestutils.c:3038)
by 0x4A1D181: g_test_run_suite (gtestutils.c:3115)
by 0x4A156EC: UnknownInlinedFun (gtestutils.c:2234)
by 0x4A156EC: g_test_run (gtestutils.c:2221)
by 0x401721: main (test_account_option.c:157)

61 (48 direct, 13 indirect) bytes in 1 blocks are definitely lost in loss record 134 of 276
at 0x4848464: calloc (vg_replace_malloc.c:1340)
by 0x49F75F0: g_malloc0 (gmem.c:163)
by 0x48C3BC7: purple_account_option_copy (purpleaccountoption.c:93)
by 0x4014BF: test_purple_account_option_copy_int (test_account_option.c:68)
by 0x4A1CC7D: UnknownInlinedFun (gtestutils.c:2933)
by 0x4A1CC7D: g_test_run_suite_internal (gtestutils.c:3021)
by 0x4A1C9E4: g_test_run_suite_internal (gtestutils.c:3038)
by 0x4A1C9E4: g_test_run_suite_internal (gtestutils.c:3038)
by 0x4A1D181: g_test_run_suite (gtestutils.c:3115)
by 0x4A156EC: UnknownInlinedFun (gtestutils.c:2234)
by 0x4A156EC: g_test_run (gtestutils.c:2221)
by 0x401721: main (test_account_option.c:157)
```
leaks in the credential manager test (times 3 for read/write/cancel tests):
```
69 (16 direct, 53 indirect) bytes in 1 blocks are definitely lost in loss record 2,427 of 3,503
at 0x484386F: malloc (vg_replace_malloc.c:393)
by 0x4A58168: g_malloc (gmem.c:130)
by 0x4A6FAB5: g_slice_alloc (gslice.c:1074)
by 0x4A700EC: g_slice_alloc0 (gslice.c:1100)
by 0x4A3BECB: g_error_allocate (gerror.c:710)
by 0x4A3C93F: UnknownInlinedFun (gerror.c:724)
by 0x4A3C93F: g_error_new_valist (gerror.c:766)
by 0x4BEE558: g_task_return_new_error (gtask.c:1941)
by 0x48D82C0: purple_credential_manager_read_password_async (purplecredentialmanager.c:492)
by 0x403634: test_purple_credential_manager_no_provider_read_password_idle (test_credential_manager.c:329)
by 0x4A4ECB1: g_idle_dispatch (gmain.c:6124)
by 0x4A4FCBE: UnknownInlinedFun (gmain.c:3444)
by 0x4A4FCBE: g_main_context_dispatch (gmain.c:4162)
by 0x4AA5597: g_main_context_iterate.constprop.0 (gmain.c:4238)
by 0x4A4F28E: g_main_loop_run (gmain.c:4438)
by 0x40369F: test_purple_credential_manager_no_provider_read_password_async (test_credential_manager.c:345)
by 0x4A7DC7D: UnknownInlinedFun (gtestutils.c:2933)
by 0x4A7DC7D: g_test_run_suite_internal (gtestutils.c:3021)
by 0x4A7D9E4: g_test_run_suite_internal (gtestutils.c:3038)
by 0x4A7D9E4: g_test_run_suite_internal (gtestutils.c:3038)
by 0x4A7E181: g_test_run_suite (gtestutils.c:3115)
by 0x4A766EC: UnknownInlinedFun (gtestutils.c:2234)
by 0x4A766EC: g_test_run (gtestutils.c:2221)
by 0x4048F6: main (test_credential_manager.c:695)
```
a leak in the image test:
```
161 bytes in 1 blocks are definitely lost in loss record 260 of 274
at 0x484386F: malloc (vg_replace_malloc.c:393)
by 0x4A55363: g_try_malloc (gmem.c:286)
by 0x4A3D630: UnknownInlinedFun (gfileutils.c:819)
by 0x4A3D630: UnknownInlinedFun (gfileutils.c:924)
by 0x4A3D630: g_file_get_contents (gfileutils.c:1027)
by 0x401890: test_image_new_from_file (test_image.c:144)
by 0x4A7DC7D: UnknownInlinedFun (gtestutils.c:2933)
by 0x4A7DC7D: g_test_run_suite_internal (gtestutils.c:3021)
by 0x4A7D9E4: g_test_run_suite_internal (gtestutils.c:3038)
by 0x4A7E181: g_test_run_suite (gtestutils.c:3115)
by 0x4A766EC: UnknownInlinedFun (gtestutils.c:2234)
by 0x4A766EC: g_test_run (gtestutils.c:2221)
by 0x40195D: main (test_image.c:172)
```
a leak in queued output stream test:
```
72 (40 direct, 32 indirect) bytes in 1 blocks are definitely lost in loss record 219 of 396
at 0x49D51EF: g_type_create_instance (gtype.c:1909)
by 0x49BAC1F: g_object_new_internal (gobject.c:2228)
by 0x49BC247: g_object_new_with_properties (gobject.c:2391)
by 0x49BCFF0: g_object_new (gobject.c:2037)
by 0x402003: test_queued_output_stream_push_bytes_async_error (test_queued_output_stream.c:219)
by 0x4A7DC7D: UnknownInlinedFun (gtestutils.c:2933)
by 0x4A7DC7D: g_test_run_suite_internal (gtestutils.c:3021)
by 0x4A7D9E4: g_test_run_suite_internal (gtestutils.c:3038)
by 0x4A7E181: g_test_run_suite (gtestutils.c:3115)
by 0x4A766EC: UnknownInlinedFun (gtestutils.c:2234)
by 0x4A766EC: g_test_run (gtestutils.c:2221)
by 0x402429: main (test_queued_output_stream.c:280)
```
and protocol xfer tests (times 3 for each test that creates a test protocol object):
```
112 (48 direct, 64 indirect) bytes in 1 blocks are definitely lost in loss record 3,430 of 3,698
at 0x49D51EF: g_type_create_instance (gtype.c:1909)
by 0x49BAC1F: g_object_new_internal (gobject.c:2228)
by 0x49BC247: g_object_new_with_properties (gobject.c:2391)
by 0x49BCFF0: g_object_new (gobject.c:2037)
by 0x40291C: test_purple_protocol_xfer_send_file_func (test_protocol_xfer.c:146)
by 0x4A7DC7D: UnknownInlinedFun (gtestutils.c:2933)
by 0x4A7DC7D: g_test_run_suite_internal (gtestutils.c:3021)
by 0x4A7D9E4: g_test_run_suite_internal (gtestutils.c:3038)
by 0x4A7E181: g_test_run_suite (gtestutils.c:3115)
by 0x4A766EC: UnknownInlinedFun (gtestutils.c:2234)
by 0x4A766EC: g_test_run (gtestutils.c:2221)
by 0x402B64: main (test_protocol_xfer.c:195)
```
and util tests (times 3 for each call to `purple_text_strip_mnemonic` in the test):
```
5 bytes in 1 blocks are definitely lost in loss record 5 of 247
at 0x484386F: malloc (vg_replace_malloc.c:393)
by 0x49F7168: g_malloc (gmem.c:130)
by 0x491975B: purple_text_strip_mnemonic (util.c:895)
by 0x4015B0: test_util_text_strip_mnemonic (test_util.c:49)
by 0x4A1CC7D: UnknownInlinedFun (gtestutils.c:2933)
by 0x4A1CC7D: g_test_run_suite_internal (gtestutils.c:3021)
by 0x4A1C9E4: g_test_run_suite_internal (gtestutils.c:3038)
by 0x4A1C9E4: g_test_run_suite_internal (gtestutils.c:3038)
by 0x4A1D181: g_test_run_suite (gtestutils.c:3115)
by 0x4A156EC: UnknownInlinedFun (gtestutils.c:2234)
by 0x4A156EC: g_test_run (gtestutils.c:2221)
by 0x401901: main (test_util.c:224)
```
and these leaks in any test that initializes the test UI:
```
4,104 bytes in 1 blocks are possibly lost in loss record 3,451 of 3,457
at 0x484386F: malloc (vg_replace_malloc.c:393)
by 0x5235B67: sqlite3MemMalloc.lto_priv.0 (sqlite3.c:25493)
by 0x5232797: UnknownInlinedFun (sqlite3.c:29181)
by 0x5232797: UnknownInlinedFun (sqlite3.c:29227)
by 0x5232797: sqlite3Malloc.lto_priv.0 (sqlite3.c:29221)
by 0x523BD8B: pcache1Alloc.lto_priv.0 (sqlite3.c:53546)
by 0x5249A8B: UnknownInlinedFun (sqlite3.c:53675)
by 0x5249A8B: allocateTempSpace (sqlite3.c:70848)
by 0x52625A6: sqlite3VdbeExec.lto_priv.0 (sqlite3.c:93857)
by 0x525CBEE: UnknownInlinedFun (sqlite3.c:87995)
by 0x525CBEE: UnknownInlinedFun (sqlite3.c:88056)
by 0x525CBEE: sqlite3_step (sqlite3.c:88045)
by 0x529B324: sqlite3_exec (sqlite3.c:131002)
by 0x48FD558: purple_sqlite3_run_migration (purplesqlite3.c:37)
by 0x48FDBB4: purple_sqlite3_run_migrations_from_resources (purplesqlite3.c:195)
by 0x48FDED9: purple_sqlite_history_adapter_run_migrations (purplesqlitehistoryadapter.c:69)
by 0x48FE7F0: purple_sqlite_history_adapter_activate (purplesqlitehistoryadapter.c:287)
by 0x48DB656: purple_history_adapter_activate (purplehistoryadapter.c:181)
by 0x48DC9BC: purple_history_manager_set_active (purplehistorymanager.c:308)
by 0x402BA8: test_ui_init_history (test_ui.c:132)
by 0x402C80: test_ui_purple_init (test_ui.c:167)
by 0x4027BB: main (test_contact.c:88)

4,368 bytes in 1 blocks are possibly lost in loss record 3,453 of 3,457
at 0x484386F: malloc (vg_replace_malloc.c:393)
by 0x5235B67: sqlite3MemMalloc.lto_priv.0 (sqlite3.c:25493)
by 0x5232797: UnknownInlinedFun (sqlite3.c:29181)
by 0x5232797: UnknownInlinedFun (sqlite3.c:29227)
by 0x5232797: sqlite3Malloc.lto_priv.0 (sqlite3.c:29221)
by 0x523BD8B: pcache1Alloc.lto_priv.0 (sqlite3.c:53546)
by 0x5240077: UnknownInlinedFun (sqlite3.c:53634)
by 0x5240077: pcache1FetchStage2 (sqlite3.c:54104)
by 0x5243E9C: UnknownInlinedFun (sqlite3.c:52671)
by 0x5243E9C: getPageNormal.lto_priv.0 (sqlite3.c:60628)
by 0x524A510: UnknownInlinedFun (sqlite3.c:60805)
by 0x524A510: btreeGetPage.lto_priv.0 (sqlite3.c:70289)
by 0x524C2F6: UnknownInlinedFun (sqlite3.c:71257)
by 0x524C2F6: sqlite3BtreeBeginTrans.lto_priv.0 (sqlite3.c:71647)
by 0x5266B3A: sqlite3VdbeExec.lto_priv.0 (sqlite3.c:93532)
by 0x525CBEE: UnknownInlinedFun (sqlite3.c:87995)
by 0x525CBEE: UnknownInlinedFun (sqlite3.c:88056)
by 0x525CBEE: sqlite3_step (sqlite3.c:88045)
by 0x48FD715: purple_sqlite3_get_schema_version (purplesqlite3.c:79)
by 0x48FD9DD: purple_sqlite3_run_migrations_from_resources (purplesqlite3.c:146)
by 0x48FDED9: purple_sqlite_history_adapter_run_migrations (purplesqlitehistoryadapter.c:69)
by 0x48FE7F0: purple_sqlite_history_adapter_activate (purplesqlitehistoryadapter.c:287)
by 0x48DB656: purple_history_adapter_activate (purplehistoryadapter.c:181)
by 0x48DC9BC: purple_history_manager_set_active (purplehistorymanager.c:308)
by 0x402BA8: test_ui_init_history (test_ui.c:132)
by 0x402C80: test_ui_purple_init (test_ui.c:167)
by 0x4027BB: main (test_contact.c:88)

4,368 bytes in 1 blocks are possibly lost in loss record 3,454 of 3,457
at 0x484386F: malloc (vg_replace_malloc.c:393)
by 0x5235B67: sqlite3MemMalloc.lto_priv.0 (sqlite3.c:25493)
by 0x5232797: UnknownInlinedFun (sqlite3.c:29181)
by 0x5232797: UnknownInlinedFun (sqlite3.c:29227)
by 0x5232797: sqlite3Malloc.lto_priv.0 (sqlite3.c:29221)
by 0x523BD8B: pcache1Alloc.lto_priv.0 (sqlite3.c:53546)
by 0x5240077: UnknownInlinedFun (sqlite3.c:53634)
by 0x5240077: pcache1FetchStage2 (sqlite3.c:54104)
by 0x5243E9C: UnknownInlinedFun (sqlite3.c:52671)
by 0x5243E9C: getPageNormal.lto_priv.0 (sqlite3.c:60628)
by 0x52499BC: UnknownInlinedFun (sqlite3.c:60805)
by 0x52499BC: UnknownInlinedFun (sqlite3.c:70289)
by 0x52499BC: btreeGetUnusedPage (sqlite3.c:70432)
by 0x524F504: allocateBtreePage.lto_priv.0 (sqlite3.c:74604)
by 0x5256209: btreeCreateTable.lto_priv.0 (sqlite3.c:77830)
by 0x5265EB2: UnknownInlinedFun (sqlite3.c:77849)
by 0x5265EB2: sqlite3VdbeExec.lto_priv.0 (sqlite3.c:96382)
by 0x525CBEE: UnknownInlinedFun (sqlite3.c:87995)
by 0x525CBEE: UnknownInlinedFun (sqlite3.c:88056)
by 0x525CBEE: sqlite3_step (sqlite3.c:88045)
by 0x529B324: sqlite3_exec (sqlite3.c:131002)
by 0x48FD558: purple_sqlite3_run_migration (purplesqlite3.c:37)
by 0x48FDBB4: purple_sqlite3_run_migrations_from_resources (purplesqlite3.c:195)
by 0x48FDED9: purple_sqlite_history_adapter_run_migrations (purplesqlitehistoryadapter.c:69)
by 0x48FE7F0: purple_sqlite_history_adapter_activate (purplesqlitehistoryadapter.c:287)
by 0x48DB656: purple_history_adapter_activate (purplehistoryadapter.c:181)
by 0x48DC9BC: purple_history_manager_set_active (purplehistorymanager.c:308)
by 0x402BA8: test_ui_init_history (test_ui.c:132)
by 0x402C80: test_ui_purple_init (test_ui.c:167)
by 0x4027BB: main (test_contact.c:88)
```

Testing Done:
Ran tests in valgrind, and all above leaks were gone except for noted `protocol_xfer` issues, and a bunch of leaks of the `PurpleBuddy`-`PurpleContact` compatibility bindings, which will go away in their entirety eventually.

Reviewed at https://reviews.imfreedom.org/r/2385/