Rethought distributed fsck. It's not really a fsck, but an expiration of
inactive repositories, where fscking is one kind of activity. That insight
let me reimplement it much more efficiently. Rather than updating all
the location logs to prove it was active, `git annex fsck` can simply and
inexpensively update an activity log. It's so cheap it'll do it by default.
The `git annex expire` command then reads the activity log and expires
(or unexpires) repositories that have not been active in the desired time
period. Expiring a repository simply marks it as dead.

Yesterday, finished making --quiet really be quiet. That sounds easy,
but it took several hours. On the `concurrentprogress` branch, I have
ascii-progress hooked up and working, but it's not quite ready for prime
time.
