The user active watch is a one-fire watch, but it is valid in the API
for the callback to explicitly remove the watch itself. In that case,
the watch will be invalid after the user removes it, and the memory
potentially freed. So make sure to not dereference the watch after
the callback is called.
https://bugzilla.gnome.org/show_bug.cgi?id=706825
To allow other clients (gnome-session, gnome-settings-daemon)
to monitor user activity, introduce a DBus interface for the
idle monitor inside mutter.
https://bugzilla.gnome.org/show_bug.cgi?id=706005
When running as a wayland compositor, we can't use the xserver's
IDLETIME, because that's updated only in response to X events.
But we have all the events ourselves, so we can just run the timer
in process.
https://bugzilla.gnome.org/show_bug.cgi?id=706005
