Previously we were indexing the full name, which allowed users to search

by full name. However, if a user has marked their profile as private, we

do not want them to be searchable by their name.
Additionally, this patch addresses two further issues:


The show_profile attribute was stored as a BooleanField, but

   there is a longstanding Haystack bug that results in boolean fields

   always being returned from Whoosh as True. This has been replaced with

   a custom BooleanField with the correct behaviour.


The show_profile as indexing the result of User.is_profile_visible(),

   which will always return False when there is no user argument

   supplied. Instead, we now store the is_private attribute of

Profile directly on the index.


Finally, the search API has been updated to strip the full name out of

results when using the database query backend (i.e., when either search

or on-the-fly indexing is disabled).

Ran unit tests.