Make the jardiff.py fully cross-platform

Make the jardiff.py fully cross-platform. Thanks a lot for help me, the script is working on Windows as well as on UNIX platforms :smile:.

I do not know how to program in Python, i'm a .Net guy, some things can get better :smile: in code

In Windows requires Cygwin. After I send another pull request with information about its installation and required package.

Thanks a lot.
Hi @JakeWharton I've tested in other machine with Windows 7 and you are correct, this change is not necessary, I'll change back and update the pull-request.