test the creation of new users

runs the ajax call, then checks that the new user isn't
staff/superuser, and can log in.
fix the existing test so that it actually works
test should not rely on the first user being the one it wants

also, it should clean itself up
user creation test triggers an edge case and an exception

This could easily happen to a real user; the referrer header is
entirely optional.
test to ensure that duplicate users cannot be created
Merge pull request #7 from solarpermit/test-new-user-creation

Test new user creation