WIP: timed login fixes

timed login is pretty broken with X session rights now. see gdm#460 (closed) for the full details. there's also a security hole there, which we're goina fix on the GDM side, but we can also plug the hole on the shell side and fix timed login behavior too.

this is still work in progress because i'm getting a traceback i need to track down and because it's targetting gnome 3-30 and not master