Still working on the git repair code. Improved the test suite, which found
some more bugs, and so I've been running tests all day and occasionally
going and fixing a bug in the repair code. The hardest part of repairing a
git repo has turned out to be reliably determining which objects in it are
broken. Bugs in git don't help (but the git devs are going to fix the one I
reported).

But the interesting new thing today is that I added some upgrade alert code
to the webapp. Ideally everyone would get git-annex and other software as
part of an OS distribution, which would include its own upgrade system -- 
But the  [survey](http://git-annex-survey.branchable.com/polls/2013/how_installed/)
tells me that a quarter of installs are from the prebuilt binaries I
distribute.

So, those builds are going to be built with knowledge of an upgrade url,
and will periodically download a small info file (over https) to see if a
newer version is available, and show an alert.

I think all that's working, though I have not yet put the info files in
place and tested it. The actual upgrade process will be a manual
download and reinstall, to start with, and then perhaps I'll automate it
further, depending on how hard that is on the different platforms.
