Fixed flake8 complaints.
Added Python 3.3 and removed Python 2.5 and Django 1.3.
Added Python 3.2 as Django also provides experimental support for it.
Use six.with_metaclass instead of some hack.
Quick fix: don't use mysql for Python3 travis test.
Conditional installation in travis.
Merge remote-tracking branch 'deschler/python3' into python3

Conflicts:
	.travis.yml
	modeltranslation/tests/__init__.py
	modeltranslation/translator.py