[bug 928359] Run unindex tasks after deleting users from cron job.

The test provided doesn't really confirm the fix. It just proves that the signal handlers we have in place should work from a request.

Testing the actual fix is a little involved:
1- While logged out, create a new question (/questions/new) with title and body: "lorem ipsum dolor sit amet"
2- During the process create a brand new user "testaccount123" or whatever.
3- When done, you should see the question in advanced search (it won't show up in basic search because it doesn't have any helpful votes on replies):
http://localhost:8000/en-US/search?q=lorem+ipsum+dolor+sit+amet&num_voted=0&num_votes=&asked_by=&answered_by=&q_tags=&created=0&created_date=&updated=0&updated_date=&sortby=0&a=1&w=2
4- Log in as a superuser, go to the admin, search for the new user and set the date_joined to over 30 days ago.
6- Run the cron job `$ ./manage.py cron remove_expired_registration_profiles`
5- Hard refresh the search results page from step 3 and the question should be gone. 

r?