Fix some (more) problems with subselects in rules. Rewriter failed to

Fix some (more) problems with subselects in rules.  Rewriter failed to
mark query as having subselects if a subselect was added from a rule
WHERE condition (as opposed to a rule action).  Also, fix adjustment
of varlevelsup so that it actually has some prospect of working when
inserting an expression containing a subselect into a subquery.