Merge branch 'tb/sanitize-decomposed-utf-8-pathname'

Merge branch 'tb/sanitize-decomposed-utf-8-pathname'

Teaches git to normalize pathnames read from readdir(3) and all
arguments from the command line into precomposed UTF-8 (assuming
that they come as decomposed UTF-8) to work around issues on Mac OS.

I think there still are other places that need conversion
(e.g. paths that are read from stdin for some commands), but this
should be a good first step in the right direction.

* tb/sanitize-decomposed-utf-8-pathname:
  git on Mac OS and precomposed unicode