Fix vacuum analyze error.

vacuum analyze on pg_type fails if bogus entries remain in pg_operator.
Here is a sample script to reproduce the problem.

drop table t1;
create table t1(i int);
drop function foo(t1,t1);
create function foo(t1,t1) returns bool as 'select true' language 'sql';
create operator = (
	leftarg = t1,
	rightarg = t1,
	commutator = =,
	procedure = foo
	);
drop table t1;
vacuum analyze;

src/backend/parser/parse_coerce.c

@@ -8,7 +8,7 @@
  *
  *
  * IDENTIFICATION
- *	  $Header: /cvsroot/pgsql/src/backend/parser/parse_coerce.c,v 2.54 2001/01/24 19:43:01 momjian Exp $
+ *	  $Header: /cvsroot/pgsql/src/backend/parser/parse_coerce.c,v 2.55 2001/02/27 07:07:00 ishii Exp $
  *
  *-------------------------------------------------------------------------
  */
@@ -225,6 +225,12 @@ can_coerce_type(int nargs, Oid *input_typeids, Oid *func_typeids)
 		if (typeInheritsFrom(inputTypeId, targetTypeId))
 			continue;
 
+		/* don't choke on references to no-longer-existing types */
+		if (!typeidIsValid(inputTypeId))
+ 		    return false;
+ 		if (!typeidIsValid(targetTypeId))
+ 		    return false;
+
 		/*
 		 * Else, try for explicit conversion using functions: look for a
 		 * single-argument function named with the target type name and