Django 1.4 Support, File System Cleanup on Avatar Removal

This pull request originated from the eldarion/django-avatar fork and includes Django 1.4 support, a post_delete signal which removes unused avatars from the file system (an issue that originated with Django 1.3), HTTPS support for Gravatar, the addition of a css class argument to the avatar template tag and the addition of testdata to distribution package so third parties can run the tests.