add tox testing infrastructure
fix test to work on python 2.6
Merge branch 'python3' of https://github.com/kaedroho/django-modelcluster into kaedroho-python3
add 'six' as a dependency
add python 3.2 and 3.3 to tox tests
Added Python 3.4 to tox settings
Added more version classifiers to setup.py