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/spi/autoinc.sql.in

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

contrib/spi/insert_username.sql.in

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

contrib/spi/moddatetime.sql.in

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

contrib/spi/refint.sql.in

@@ -2,11 +2,11 @@ DROP FUNCTION check_primary_key ();
 DROP FUNCTION check_foreign_key ();
 
 CREATE FUNCTION check_primary_key ()
-	RETURNS opaque
+	RETURNS trigger
 	AS 'MODULE_PATHNAME'
 	LANGUAGE 'C';
 
 CREATE FUNCTION check_foreign_key ()
-	RETURNS opaque
+	RETURNS trigger
 	AS 'MODULE_PATHNAME'
 	LANGUAGE 'C';

contrib/spi/timetravel.sql.in

@@ -2,7 +2,7 @@ DROP FUNCTION timetravel();
 DROP FUNCTION set_timetravel(name, int4);
 
 CREATE FUNCTION timetravel() 
-	RETURNS opaque 
+	RETURNS trigger 
 	AS 'MODULE_PATHNAME'
 	LANGUAGE 'C';