v1.3.5-1-g74adbbc-dirty

Better handling of directory mod times.

Mirror is fundamentally based on mod times, i.e. latest mod time wins.

This works great for files, but directories are a bit different, because
any new/changed file in a directory, updates the directory's own mod
time to an OS-generated value.

In general we don't want to bother with keeping these in-sync across
local/remote, so now we explicitly ignore this case.

Deletions also don't work well with mod times, b/c a deletion doesn't
really have a time in the file system anymore; previously we added the
old mod time + 1 second immediately when the delete happened, but this
could result in an ignored write, hwen our "now + 1 second" hueristic
was artificially ahead of an actual now + < 1 second write on the
just-deleted file.

We still need to fudge with mod times on "deleted then restored via
mv" files, to ensure their still-in-the-past-b/c-it-was-restored mod
time "wins" over the deletion mark, so we recognize when that is
happening and bump the restored file's mod time ahead by 1 second.