Fix some of the GLib mainloop implementation in compiz
1. Don't use Glib::RefPtr for sources as they are broken (unref will cause a crash on a destroyed source)
2. Don't g_main_context_iteration in order to flush the event queue
3. Use XFlush instead
4. Handle signals using glib's signal sources so that they are safely dispatched back to the mainloop
5. Enabled failing Xig Tests
Merge lp:~smspillaz/compiz-core/compiz-core.glib-mainloop-fixes