Infrastructure for deducing Param types from context, in the same way

that the types of untyped string-literal constants are deduced (ie,
when coerce_type is applied to 'em, that's what the type must be).
Remove the ancient hack of storing the input Param-types array as a
global variable, and put the info into ParseState instead.  This touches
a lot of files because of adjustment of routine parameter lists, but
it's really not a large patch.  Note: PREPARE statement still insists on
exact specification of parameter types, but that could easily be relaxed
now, if we wanted to do so.

src/backend/optimizer/prep/prepunion.c

@@ -14,7 +14,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepunion.c,v 1.93 2003/04/24 23:43:09 tgl Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/optimizer/prep/prepunion.c,v 1.94 2003/04/29 22:13:09 tgl Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -418,7 +418,8 @@ generate_setop_tlist(List *colTypes, int flag,
 		}
 		else
 		{
-			expr = coerce_to_common_type(expr,
+			expr = coerce_to_common_type(NULL, /* no UNKNOWNs here */
+										 expr,
 										 colType,
 										 "UNION/INTERSECT/EXCEPT");
 			colTypmod = -1;