added support for non-ascii directories and file names

[xarx00]

This fix allows support for non-ascii filenames, both in workdir and repos. For instance, when your workdir contains non-ascii (0-255) characters, git.Repo.clone_from() didn't work.

Implementation:
It turned out that the amount of necessary changes is not big. The main problem was in that git.compat.defenc was set to sys.getdefaultencoding() instead of sys.getfilesystemencoding().
sys.getfilesystemencoding() requires Python 2.3. The from builtins import str fixes several str(epath) etc. conversions that were causing UnicodeEncodeError. I have no idea what python2 version is necessary for that.

I have tested the fix on Windows7 Pro x64, both with Python 2.7.13 and 3.7.3.

[codecov-io]

Codecov Report

Merging #860 into master will decrease coverage by 1.24%.
The diff coverage is 80%.

@@            Coverage Diff             @@
##           master     #860      +/-   ##
==========================================
- Coverage   94.79%   93.54%   -1.25%     
==========================================
  Files          59       59              
  Lines        9603     9607       +4     
==========================================
- Hits         9103     8987     -116     
- Misses        500      620     +120

Impacted Files	Coverage Δ
git/repo/base.py	94.12% <100%> (-1.25%)	⬇️
git/compat.py	41.21% <75%> (-23.61%)	⬇️
git/test/test_util.py	90.41% <0%> (-8.22%)	⬇️
git/test/lib/asserts.py	61.53% <0%> (-7.7%)	⬇️
git/test/lib/helper.py	85.95% <0%> (-6.18%)	⬇️
git/test/test_base.py	96.59% <0%> (-2.28%)	⬇️
git/test/test_git.py	96.64% <0%> (-2.24%)	⬇️
git/objects/submodule/base.py	93.08% <0%> (-1.42%)	⬇️
git/test/test_submodule.py	97.93% <0%> (-1.32%)	⬇️
... and 13 more

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[Byron]

Thanks a lot, and I would love to merge this. However, it appears the PR breaks a single test in Py 2.7, and I am not entirely sure these are related. So I am merging to test it in master, and revert as needed.

[Byron]

Unfortunately the build still fails on top of master for the same reason as before. I have no idea why this is happening.
What do you recommend?