small Django tweak to make usernames 75 chars long.  In order to work with old installationa and new installations, generated a django.contrib.auth schema change, but put it under the registration folder.
adding comments
Merge branch 'username_length' of git://github.com/bcipolli/ka-lite into bcipolli-username_length

Conflicts:
	docs/DJANGO-CHANGES.txt
	kalite/settings.py