Ghar for Windows

Here's the Windows support code I mentioned in my earlier email. It basically monkey-patches the `os` module, so that symlink-related functions work properly (which requires Windows Vista or higher, BTW). The patches are only needed under Python 2.x.

I've kept the main ghar code clean, and only introduced a single conditional import of a `ghar_win` module. I'm not particularly proud of the code in that module, but it seems to work fairly well.

If you'd like to merge it, that'd be nice. I'm also completely fine with keeping this a separate branch, though :) And, of course, if you feel like making any comments, feel free!