Withdrawn mentors not handled properly

[sagesharp]

When a mentor withdraws from a project, the following things should happen:

1. they should no longer be listed as a mentor for the project on the alums page
2. they should no longer receive emails related to the project (e.g. internship emails sent every two weeks, or requests for mentor feedback)
3. they should not have the internship listed on their dashboard
4. they should not be allowed to give mentor feedback (even by guessing the URL for the feedback)
5. they should not be allowed to reject or approve other mentors for that project (even by guessing the URL for approve/reject)
6. they should not show up on the active internship contacts list
7. they should not show up on the the approved mentors contacts list for the mentors' mailing list (unless they have an approval for another project)

Right now, at least (1) is not true. When I mark a MentorApproval as Withdrawn through the Django administrator interface, the mentor still shows up on the alums page. That makes me suspicious that (2-7) might also be wrong.

Audit the code that does query lookups on MentorApproval. Should those places filter by approved()?