Add a bunch of pseudo-types to replace the behavior formerly associated

with OPAQUE, as per recent pghackers discussion.  I still want to do some
more work on the 'cstring' pseudo-type, but I'm going to commit the bulk
of the changes now before the tree starts shifting under me ...

contrib/noupdate/noup.sql.in

@@ -1,6 +1,6 @@
 DROP FUNCTION noup ();
 
 CREATE FUNCTION noup ()
-	RETURNS opaque
+	RETURNS trigger
 	AS 'MODULE_PATHNAME'
 	LANGUAGE 'C';