Remove no-longer-needed restriction against referencing system

attributes in a FieldSelect node --- all the places that manipulate
these work just fine with system attribute numbers.  OK, it's a new
feature, so shoot me ...

src/backend/parser/parse_func.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/parser/parse_func.c,v 1.96 2000/12/27 23:59:11 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/parser/parse_func.c,v 1.97 2001/01/23 02:32:26 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -1479,11 +1479,6 @@ setup_field_select(Node *input, char *attname, Oid relid)
 
 	attno = get_attnum(relid, attname);
 
-	/* XXX Is there still a reason for this restriction? */
-	if (attno < 0)
-		elog(ERROR, "Cannot reference attribute '%s'"
-			 " of tuple params/return values for functions", attname);
-
 	fselect->arg = input;
 	fselect->fieldnum = attno;
 	fselect->resulttype = get_atttype(relid, attno);