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.)

mediagoblin/db/migrations.py

@@ -709,6 +709,7 @@ def create_moderation_tables(db):
 
     db.commit()
 
+
 @RegisterMigration(19, MIGRATIONS)
 def drop_MediaEntry_collected(db):
     """
@@ -739,16 +740,15 @@ def add_metadata_column(db):
 
 class PrivilegeUserAssociation_R1(declarative_base()):
     __tablename__ = 'rename__privileges_users'
-    user_id = Column(
+    user = Column(
         Integer,
         ForeignKey(User.id),
         primary_key=True)
-    privilege_id = Column(
+    privilege = Column(
         Integer,
         ForeignKey(Privilege.id),
         primary_key=True)
 
-
 @RegisterMigration(21, MIGRATIONS)
 def fix_privilege_user_association_table(db):
     """
@@ -760,6 +760,8 @@ def fix_privilege_user_association_table(db):
 
     privilege_user_assoc = inspect_table(
         metadata, 'core__privileges_users')
+
+    if db.bind.url.drivername == 'sqlite':
         PrivilegeUserAssociation_R1.__table__.create(db.bind)
         db.commit()
 
@@ -770,12 +772,16 @@ def fix_privilege_user_association_table(db):
             # The columns were improperly named before, so we switch the columns
             user_id, priv_id = row['core__privilege_id'], row['core__user_id']
             db.execute(new_privilege_user_assoc.insert().values(
-            user_id=user_id,
+                user=user_id,
-            privilege_id=priv_id))
+                privilege=priv_id))
 
         db.commit()
 
         privilege_user_assoc.drop()
         new_privilege_user_assoc.rename('core__privileges_users')
 
+    else:
+        privilege_user_assoc.c.user_id.alter(name="privilege")
+        privilege_user_assoc.c.privilege_id.alter(name="user")
+
     db.commit()

mediagoblin/db/models.py

@@ -877,11 +877,11 @@ class PrivilegeUserAssociation(Base):
 
     __tablename__ = 'core__privileges_users'
 
-    user_id = Column(
+    user = Column(
         Integer,
         ForeignKey(User.id),
         primary_key=True)
-    privilege_id = Column(
+    privilege = Column(
         Integer,
         ForeignKey(Privilege.id),
         primary_key=True)