Fix a crash when hovering over an exceptionally long URL (4074 characters,
but it might be different for you) in a gtkimhtml widget (such as the IM
window).

This was reported on the support mailing list:
http://pidgin.im/pipermail/support/2013-March/012980.html
http://pidgin.im/pipermail/support/2013-March/012981.html

Repro steps:
1. "gdb pidgin"

2. "break gdk_x_error"
You'll probably need to type "y" to make breakpoint pending on future shared library load. (Or you could run first then add the breakpoint.)

3. "run --sync"
--sync probably isn't actually necessary. Theoretically it should make the backtrace more useful. Like, maybe it could actually show the Pidgin calls that trigger the problem? Or maybe the problem call starts from the gtk main loop, so there would never be Pidgin code in the backtrace? It's also possible we don't pass our args to the right places to make --sync work.

4. "cont"
I hit the breakpoint at startup for some reason. I've just been continuing past it. Doesn't seem to affect anything.

5. Open an IM window.

6. Paste a long URL.

7. Mouse over the long URL.

8. The breakpoint is hit.

9. "bt"

#0 gdk_x_error (display=0x740e30, error=0x7fffffffbc20)
at /build/buildd/gtk+2.0-2.24.13/gdk/x11/gdkmain-x11.c:458
#1 0x00007ffff73b94f6 in _XError () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#2 0x00007ffff73b6741 in ?? () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#3 0x00007ffff73b6785 in ?? () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#4 0x00007ffff73b7378 in _XReply () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#5 0x00007ffff73b2d3d in XSync () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#6 0x00007ffff73b2dcb in ?? () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#7 0x00007ffff73b9e2f in ?? () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#8 0x00007ffff7395d14 in XCreatePixmap () from /usr/lib/x86_64-linux-gnu/libX11.so.6
#9 0x00007ffff62bd0d2 in _gdk_pixmap_new (drawable=0x186ec60, width=width@entry=32774, height=25, depth=24,
depth@entry=-1) at /build/buildd/gtk+2.0-2.24.13/gdk/x11/gdkpixmap-x11.c:175
#10 0x00007ffff6289617 in IA__gdk_pixmap_new (drawable=drawable@entry=0x186ec60, width=width@entry=32774,
height=, depth=depth@entry=-1) at /build/buildd/gtk+2.0-2.24.13/gdk/gdkpixmap.c:249
#11 0x00007ffff6297036 in gdk_window_begin_implicit_paint (rect=0x7fffffffbed0, window=0x186ec60)
at /build/buildd/gtk+2.0-2.24.13/gdk/gdkwindow.c:2779
#12 gdk_window_process_updates_internal (window=0x186ec60) at /build/buildd/gtk+2.0-2.24.13/gdk/gdkwindow.c:5574
#13 0x00007ffff6299201 in IA__gdk_window_process_all_updates ()
at /build/buildd/gtk+2.0-2.24.13/gdk/gdkwindow.c:5696
#14 0x00007ffff6299269 in gdk_window_update_idle (data=)
at /build/buildd/gtk+2.0-2.24.13/gdk/gdkwindow.c:5322
#15 0x00007ffff6276e77 in gdk_threads_dispatch (data=0x1a45c40) at /build/buildd/gtk+2.0-2.24.13/gdk/gdk.c:512
#16 0x00007ffff53d8ab5 in g_main_context_dispatch () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#17 0x00007ffff53d8de8 in ?? () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#18 0x00007ffff53d91e2 in g_main_loop_run () from /lib/x86_64-linux-gnu/libglib-2.0.so.0
#19 0x00007ffff663ec77 in IA__gtk_main () at /build/buildd/gtk+2.0-2.24.13/gtk/gtkmain.c:1271
#20 0x0000000000499950 in main (argc=1, argv=0x7fffffffe538) at gtkmain.c:933

This is the message it prints when it exits:
The program 'Pidgin' received an X Window System error.
This probably reflects a bug in the program.
The error was 'BadAlloc (insufficient resources for operation)'.
(Details: serial 14454 error_code 11 request_code 53 minor_code 0)
(Note to programmers: normally, X errors are reported asynchronously;
that is, you will receive the error a while after causing it.
To debug your program, run it with the --sync command line
option to change this behavior. You can then get a meaningful
backtrace from your debugger if you break on the gdk_x_error() function.)

I think it's kinda lame that gdk/gtk/xlib/whatever barfs when we give it a
ridiculously wide pango layout, but whatever. I'm assuming this problem is
gtkimhtml specific, and so I don't want to spend a whole lot of time fixing
it. As an easy fix I want to just truncate the URL displayed in the tooltip
to 200 characters.

Here's an example URL that I used to trigger the crash:
http://www.example.com/?%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%30123456789012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789%3012345678901234567890123456789012345678901234567890123456789012345678