Bus: Add custom code for the AddWatch method
Bus: Add custom code for the AddWatch method

For now, this is better than making everyone use AddWatchFull, even
though the value for G_PRIORITY_DEFAULT is hardcoded.

https://bugzilla.gnome.org/show_bug.cgi?id=721985

gstreamer-sharp/gstreamer-sharp,GStreamer/gstreamer-sharp,freedesktop-unofficial-mirror/gstreamer__gstreamer-sharp,gstreamer-sharp/gstreamer-sharp,freedesktop-unofficial-mirror/gstreamer__gstreamer-sharp,GStreamer/gstreamer-sharp,gstreamer-sharp/gstreamer-sharp,freedesktop-unofficial-mirror/gstreamer__gstreamer-sharp,GStreamer/gstreamer-sharp