StTextureCache: don't crash if we fail to allocate a framebuffer

It's possible that FBO creation fails due to hw limits or the
driver not exposing the EXT_framebuffer_object extension.
In that case, just give up on creating square icons.

https://bugzilla.gnome.org/show_bug.cgi?id=724977
NetworkMenu: destroy the wifi dialog when the associate device disappears

When the device is removed by NetworkManager, we can't use it
to connect, so the dialog is useless and should be destroyed.

https://bugzilla.gnome.org/show_bug.cgi?id=723935
search: destroy result actors before forgetting about them

We can't let live (ie, never destroyed) actors undergo GC, because
they will emit :destroy signals during finalization and assert/crash
libmozjs. Properly destroy all actors before letting the GC
free them.

https://bugzilla.gnome.org/show_bug.cgi?id=724798
search: survive the provider reporting the wrong number of metas

If a provider crashes during GetResultMetas, or returns the wrong
number of metas, report it as failing but don't cause a JS exception.

https://bugzilla.gnome.org/show_bug.cgi?id=725020
TelepathyClient: destroy an existing account notification when the user goes offline

We already filter new notifications caused by the explicit
user action, but we don't do so for changes to existing
notifications.

https://bugzilla.gnome.org/show_bug.cgi?id=723976