explicitly configure MIDDLEWARE_CLASSES for django tests

Django 1.7 removed these classes from the default settings
added support for Django 1.5+ custom user models
added Django 1.7 to the test matrix
Merge branch 'feature/django-1.7-fixes' into feature/enable-django-1.7-tests
switched to py.test due to better support for Django 1.7
disabled Django 1.7 for Python 2.6
refactored test matrix to hopefully make Django matrix builds work on travis
Handle Django 1.3, which does not have a "IGNORABLE_404_URLS" setting by default
django.conf.urls.defaults has been deprecated in Django 1.4, not in 1.3
removed Django 1.2 from our build matrix
removed last traces of nose
remove Python2-inly dependencies from requirements-base.txt
pinned the versions of py.test related dependencies
Bumped version to 1.3