Add missing #include directive: pg_constraint.h declares some functions

whose prototypes include the "List" type, so it ought to include the
list header file.

src/include/catalog/pg_constraint.h

@@ -8,7 +8,7 @@
  * Portions Copyright (c) 1996-2006, PostgreSQL Global Development Group
  * Portions Copyright (c) 1994, Regents of the University of California
  *
- * $PostgreSQL: pgsql/src/include/catalog/pg_constraint.h,v 1.22 2006/03/05 15:58:54 momjian Exp $
+ * $PostgreSQL: pgsql/src/include/catalog/pg_constraint.h,v 1.23 2006/06/28 22:11:01 neilc Exp $
  *
  * NOTES
  *	  the genbki.sh script reads this file and generates .bki
@@ -19,6 +19,8 @@
 #ifndef PG_CONSTRAINT_H
 #define PG_CONSTRAINT_H
 
+#include "nodes/pg_list.h"
+
 /* ----------------
  *		postgres.h contains the system type definitions and the
  *		CATALOG(), BKI_BOOTSTRAP and DATA() sugar words so this file