HttpResponse objects via authenticate() will now stop view execution
* Previously, if authenticate() returned an HttpResponse the view would
  continue with execution and display results to unauthenticated users.
* Now the response from authenticate() is stored and if something exists
  (which needs to be a response) execution is stopped and that response
  is sent directly to the user.
Merge pull request #20 from whalesalad/master

HttpResponse objects via authenticate() will now stop view execution