TODO
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* Git thinks that filenames are bytestreams, not character sequences.
  http://article.gmane.org/gmane.comp.version-control.git/122860

* Git can not work across different encodings, and admits as much.
  Then again Subversion can't either.

* Our only hope is to ask Git for bytestreams and apply some heuristics
  as to the encoding and composition used.

* ATM, setuptools-git returns files by their OS path, not the POSIX
  path that is returned by Git. It also resolves symbolic links within
  the same repository.

* We might get away with passing along the bytestreams in Python 2,
  but in Python 3 we must return Unicode.

* For passing through non-UTF-8 filenames under Python 3, use the
  'surrogateescape' error handler.