Always run tests in DEBUG, to pick up templatetags problems
Very hacky test for mail_subscribers management command

Now I have tests, I can refactor it
PEP 8
Ensure we only send the oldest, unsent email
Move bulk of mail_subscribers command into the model layer
Remove pointless print statement
Moving code for getting the next post to email into models.py
Don't pointlessly load all the posts
django.conf.urls.defaults is deprecated