[bug 904732] Update to Django 1.4.6

This updates playdoh-lib and picks up the Django update as well as a
bunch of other stuff:

91561d9 Update to Django 1.4.6  r=r1cky
198b178 Merge pull request #42 from dpoirier/update-tower
e8e6095 Update tower
77d2cc7 Merge pull request #36 from jsocol/arecibo
54be25a Merge pull request #40 from peterbe/upgrade-django-session-csrf
963f25c upgrade django-session-csrf for safer keys
ba468e6 upgrading django-session-csrf to avoid possible
MemcachedKeyLengthError, r=Osmose
d5db036 Drop django-arecibo.