[pypy-issue] Issue #3118: '..' becoming b'..' when using pip install (pypy/pypy)

[mattip]

New issue 3118: '..' becoming b'..' when using pip install
https://bitbucket.org/pypy/pypy/issues/3118/becoming-b-when-using-pip-install

mattip:

Reported on IRC, via this gist [https://gist.github.com/squeaky-pl/2920bb5f472f70346c57e6a859ecda04](https://gist.github.com/squeaky-pl/2920bb5f472f70346c57e6a859ecda04)

Running `HGPYTHON3=1 <path/to/pypy3> -m pip install mercurial==5.0.2` errors when calling `with open(os.path.join(os.path.join(os.path.dirname(__file__), '..'), 'bdiff.c')) as f:`, the error is that somehow `'..'` is becoming `b'..'`