Python 3.3 support

I have gone through git-fat and added support for Python 3.3.  It mostly consisted of encoding fixes, since 3.3 now has strict string encoding requirements. I have done some testing on my machine, and it seems to be working correctly, but I have not tested across platforms or across versions of Python.  It is entirely possible that these changes break 2.7 compatibility.

I have also rather expanded upon the test script to make it exercise a broader subset of the git-fat functionality. Those changes should be relatively benign, but may or may not be in line with your intent for the script.