gnome-shell currently initiates an automatic login attempt if
timed login is enabled and the timed login animation completes.
Unfortunately, if animations are disabled (as is the case for
virtual machines) then the timed login animation will complete
instantly, and timed login will proceed immediately after gnome-shell
has noticed the user is idle for 5 seconds.
This commit addresses that problem by initiating timed login and the
animation from a main loop timeout, instead of using the tweener api.
9ef1bc7273