When a superuser does GRANT or REVOKE on an object he doesn't own,

process the command as though it were issued by the object owner.
This prevents creating weird scenarios in which the same privileges
may appear to flow from different sources, and ensures that a superuser
can in fact revoke all privileges if he wants to.  In particular this
means that the regression tests work when run by a superuser other than
the original bootstrap userid.  Per report from Larry Rosenman.