Python 3.3 compatibility

* decode() before running regular expressions and other operations that require strings, not buffers
* Use recent version of django-tastypie that is Python 2.6+ and 3.3+ compatible
* Remove python-memcached dependency (it's not a dependency)

The more recent django-tastypie is Django 1.5+ only. Do we really need to support Django 1.4? (Dropping 1.4 also means we can remove some 1.4 shims from the code.)