Switch "user_id" to "privilege" and "privilege_id" to "user".

Switch "user_id" to "privilege" and "privilege_id" to "user".

This builds on the previous code Natalie wrote, but makes some changes:
 - More direct alterations for non-sqlite code
 - In both cases, I've made it so that we switched the field names from
   privilege_id and user_id to user and privilege respectively.  This
   way we can do the name swap, but in one case it's "easy": just
   changing the name.  (In the sqlite case it's still tricky though.)