Fix admin login page

This fixes the admin login page so we never ever see it and/or get stuck
there and have to manually type in a url into the urlbar.

To test

1. `./manage.py runserver`
2. make sure you're not signed in
3. go to `/admin`
4. notice how it redirects you to the CORRECT login page -- rejoice!
5. login and notice how it bumps you to the admin immediately -- rejoice!
6. logout and notice how you go back to the CORRECT login page -- rejoice!
7. do a happy dance

r?