qulogic/pidgin

Add an active-provider-changed signal to PurpleCredentialManager

Testing Done:
Compiled and ran the unit tests.

Reviewed at https://reviews.imfreedom.org/r/307/
nullclient = executable('nullclient', 'nullclient.c', 'defines.h',
c_args : ['-DSTANDALONE'],
dependencies : [libpurple_dep, glib])