kqueue: fix a potential deadlock

In case an object is already monitored, we lock then return without
unlocking it which can then result in a self deadlock. So properly
unlock before returning.

https://bugzilla.gnome.org/show_bug.cgi?id=721074
gobject.py: Don't install frame filters when GDB does not support them

Stock GDB (both versions 7.0 and 7.1) does not come with the new
backtrace code and python API. To prevent an ugly python backtrace when
auto-loading gobject.py, let's catch the exception and not register the
FrameWrapper and the FrameFilter.

https://bugzilla.gnome.org/show_bug.cgi?id=613732
Merge branch 'glib-2-38' of git://git.gnome.org/glib into v2-38-stable