Add a more realistic fake session, so we can call admin pages.

Admin tries to call set_test_cookie, which we didn't have and couldn't add
to a plain dict.
Allow explicitly passing file parameters to fast_dispatch.

Sometimes the guessing of file/POST params was wrong, or you want to
explicitly pass a string as a file parameter to test what happens with
uploads that aren't files in file fields.
Convert exception messages to unicode to avoid encoding errors.
Assign the view to the response, so we can check for values on it
Allow passing parameters for reverse() to assert_login_required
Remove unused code