Handle focus-out events, watch for something that looks like synergy

Handle focus-out events, watch for something that looks like synergy
stealing the cursor when it moves to another screen, and unfocus the
window if this happens. Makes synergy across multiple scrotwm machines
much nicer, as you only get the focus window border on one screen at
a time.

Also, unfocus_all is a sledgehammer, don't use it so much.