Revert "Add Python 3.3 to .travis.yml"

This reverts commit 4dee3b787d040613fa632c3300a29def955ca128.

Django 1.4.x doesn't support Python 3.x, so the .travis.yml file needs to
specify that the combination of Python 3.3 and Django 1.4.x should not be
tested.
PEP 8 style fixes
Change __unicode__ -> __str__ and add python_2_unicode_compatible decorator
Disable standard_library import hooks for pychecker
Add future == 0.8.2 to requirements; remove dependency for setup.py