manage.py create_test_db add -f force option

I tried to get this branch to only include the manage.py changes that I made, but I'm having trouble rebasing, so it's got all the test changes too. It's probably best to accept the test pull request first, then ping me, and I'll put in a new pull request from my master branch with only the manage.py changes. 

In the mean time, you can of course still view the manage.py changes I made here. Or accept it from this pull request if you'd like. Your call.