Use six for pulling in unquote.
Use six for pulling in unquote.

This change updates the TFS implementation to get `urllib2.unquote` from
`six.moves`, for compatibility with Python 3.

Testing Done:
Loaded the module in a Python 3 environment.

Reviewed at https://reviews.reviewboard.org/r/8632/

reviewboard/rbtools,reviewboard/rbtools,reviewboard/rbtools