Preliminary Python 3 support

I've got the (very basic) unit tests passing under Python 2.7 and Python 3.4. (As an aside, they should work on 3.3 too, but I need to reinstall it on my mac so I'm not trying it out just yet.)

I included the six.py file within the code base, since there weren't any dependencies and I figured there's no reason to add one now.

The only non-import non-syntax change had to do with URI parsing in the constructor of ServerProxy. The functions being used were internal to urllib, undocumented, and not in Python 3. I used urlparse and basically guessed what everything was. I would not trust any of that code until I write a bunch of tests for it.

Whoops, I forgot to make another branch for these changes. Also please forgive the copious whitespace trimming.