Use the more modern six library to handle urllib, cStringIO, and cPickle.
The urlparse, urllib, and urllib2 modules have been significantly reworked in

Python 3 to provide a much more consistent interface.
Additionally, the 'fast' versions of StringIO and pickle are now merged with

the 'slow' versions, so in the future we'll be able to just use io.StringIO and

pickle without the fallbacks.
six has some adaptations to help with this for the time being. It's not as

pretty as I would like, but it works.

Ran djblets unit tests.
Ran Review Board unit tests.