screensaver logout should be even more insistent

[jdreed]

Apparently there's still sometimes wackiness going on in that various apps block the logout. Rather than having separate tokens/no-tokens code as we do now, we should consider a non-blocking loop that looks to see if the session appears to be ending, and after 15 seconds, gives up and pkill's schroot. A force-logout only has to make cursory attempt to save your data. We could do something stupid/clever with a SIGALRM, or better ("better") yet, listen on DBus to see if things appear to be ending.