Add a dependency on 'six'

Review Request #6584 — Created Nov. 13, 2014 and submitted — Latest diff uploaded

Information

RBTools
master
e9de5ab...

Reviewers

In order to support both Python 2.x and 3.x without making too many changes, we
need to use the six library. This change adds the dependency.

Ran setup.py develop and saw the right packages install.