Don't always make every htauth user a superuser

[ejucovy]

Right now when a user logs in through the htauth backend, she's marked as both staff and superuser.

Instead (particularly after implementing htgroup support, #1) the user should not be marked as a superuser -- except, perhaps, if the user is in some specially-flagged htgroup entry that denotes superuser status.

I think the user should still be marked as staff though. Or possibly this behavior should be a configurable settings, HTAUTH_USERS_ARE_STAFF = True.