um-utils: Sync up with gnome-control-center

gnome-control-center 11382d24 (Chris Cummins)
gnome-control-center 2714908b (Robert Roth)

https://bugzilla.gnome.org/show_bug.cgi?id=700702
account: Fix two segfaults in dispose

- Don't unref transfer-none accountservice objects
- Make sure we don't run the realmd disappeared callback

https://bugzilla.gnome.org/show_bug.cgi?id=700376