register hooks in run!

In preparation of daemonizing. Inotify hooks (and I assume, others)
are lost when fork()ing.
syncer: don't pass paths to unison and capture unison output

unison treats passed paths as directories, which ends up bad when we
pass a deleted *file*.
fix SystemExit and capture exception backtraces
move definition of cachedir into oncotrunk.rb, also fix unison command line
implement daemon mode (is the default now)