Think I'm really finished with adjusted branches now. Fixed a bug in
annex symlink calculation when merging into an adjusted branch. And, fixed
a race condition involving a push of master from another repository.

While `git annex adjust --unlock` is reason enough to have adjusted
branches, I do want to at some point look into implementing `git annex
adjust --hide-missing`, and perhaps rewrite the view branches to use
adjusted branches, which would allow for updating view branches when
pulling from a remote.

Also, turns out Windows supports hard links, so I got annex.thin working
on Windows, as well as a few other things that work better with hard links.
