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.
Is this change needed? Everything that happens after here is string manipulation which doesn't require OS-specific separators. I would think the only thing that was broken was the paths.