I've gotten the `bs` branch to build everything again. Was not trivial,
the diff is over 7000 lines.

Had hoped this was a mechanical enough conversion it would not introduce
many bugs, but the test suite quickly found a lot of problems. So that
branch is not ready for merging yet.

I'm considering making a library that's like
[filepath](http://hackage.haskell.org/package/filepath) but for
RawFilePath. That would probably speed git-annex up by another 5% or so,
in places where it currently has to convert back to FilePath.