Fixed several problems with v6 mode today. The assistant was doing some
pretty wrong things when changes were synced into v6 repos, and that
behavior is fixed. Also dealt with a race that caused updates made to the
keys database by one process to not be seen by another process.
And, made `git annex add` of a unlocked pointer file not annex the pointer
file's content, but just add it to git as-is.

Also, Thowz pointed out that adjusted branches could be used to locally adjust
where annex symlinks point to, when a repository's git directory is not in
the usual location. I've added that, as `git annex adjust --fix`. It
was quite easy to implement this, which makes me very happy with the
adjusted branches code!