Add backports.os fsencode/fsdecode

[pombredanne]

Pi's backport of os.fsencode and os.fsdecode to Python 2 @ https://github.com/pjdelport/backports.os would be a great addition and is the only backport of these rather complex-to-get-right functions that works on Python 2. (I tested it extensively with https://github.com/nexB/scancode-toolkit and we are planning the Python 3 port aboutcode-org/scancode-toolkit#295 )

I would be a must have in python-future IMHO

[jayvdb]

Its test suite fails fairly comprehensively on AppVeyor ;-)

See PiDelport/backports.os#13

[jayvdb]

Note that a significant part of backports.os is copied exactly from https://github.com/etrepum/pyutf8 . invalid_utf8_indexes is the copied bit.

Its test suite passes on Python 2, but not on Python 3 which is understandable as it hasn't been touched since 2012 , seven years ago, and the code itself hasnt been touched since 2010.

It needs some lovin.