The webapp now fully handles repairing damage to the repository.

Along with all the git repository repair stuff already built, I added
additional repairs of the git-annex branch and git-annex's index file.
That was pretty easy actually, since git-annex already handles merging
git-annex branches that can sometimes be quite out of date. So when git repo
repair has to throw away recent changes to the git-annex branch, it just
effectively becomes out of date. Added a `git annex fsck --fast` run to
ensure that the git-annex branch reflects the current state of the
repository.

When the webapp runs a repair, it first stops the assistant from committing
new files. Once the repair is done, that's started back up, and it runs a
startup scan, which is just what is needed in this sitation; it will add
any new files, as well as any old files that the git repository damange
caused to be removed from the index.

Also made `git annex repair` run the git repository repair code, 
for those with a more command-line bent. It can be used in non-git-annex
repos too!

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So, I'm nearly ready to wrap up working on disaster recovery. Lots has been
accomplished this month. And I have put off making a release for entirely
too long!

The big missing piece is repair of git remotes located on removable drive.
I may make a release before adding that, but removable drives are probably
where git repository corruption is most likely to occur, so I certainly
need to add that.

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Today's work was sponsored by Scott Robinson.