Operation on closed file

[stardust85]

We see intermittent test https://travis-ci.org/codeinn/vcs/jobs/110129783#L350, probably caused by race condition in subprocessio library. This library is used only in one place (GitRepository in git backend).

I propose to change subprocessio.py to standard pypi module 'subprocess32'. It's python 2.4+ backport of subprocess standard module from python 3.

Makes sense?

[stardust85]

I also use subprocess in perforce backend, so switch to subprocess32 will be super-easy there, it's backwards compatible

[marcinkuzminski]

Subprocessio is a very special module a non-blocking Subprocess lib that uses threads to read in/out. It cannot be replaced by subprocess32 unfortunetly