hmm.  i feel like this might be okay for now, but https://docs.djangoproject.com/en/dev/topics/cache/#cache-key-warnings says
```
Memcached, the most commonly-used production cache backend, does not allow cache keys longer than 250 characters or containing whitespace or control characters, and using such keys will cause an exception. To encourage cache-portable code and minimize unpleasant surprises, the other built-in cache backends issue a warning 
```
so I think we should get encode all whitespace and limit to 250 chars?