Define the right-hand input of AT TIME ZONE as a full a_expr instead of

c_expr.  Perhaps the restriction was once needed to avoid bison errors,
but it seems to work just fine now --- and even generates a slightly
smaller state machine.  This change allows examples like
SELECT '13:45'::timetz AT TIME ZONE '-07:00'::interval;
to work without parentheses around the right-hand input.

src/backend/parser/gram.y

@@ -11,7 +11,7 @@
  *
  *
  * IDENTIFICATION
- *	  $PostgreSQL: pgsql/src/backend/parser/gram.y,v 2.487 2005/04/07 01:51:38 neilc Exp $
+ *	  $PostgreSQL: pgsql/src/backend/parser/gram.y,v 2.488 2005/04/23 17:22:16 tgl Exp $
  *
  * HISTORY
  *	  AUTHOR			DATE			MAJOR EVENT
@@ -6070,7 +6070,7 @@ opt_interval:
 a_expr:		c_expr									{ $$ = $1; }
 			| a_expr TYPECAST Typename
 					{ $$ = makeTypeCast($1, $3); }
-			| a_expr AT TIME ZONE c_expr
+			| a_expr AT TIME ZONE a_expr
 				{
 					FuncCall *n = makeNode(FuncCall);
 					n->funcname = SystemFuncName("timezone");