Update TODO list.

Author: bmomjian

doc/TODO

@@ -1,6 +1,6 @@
 TODO list for PostgreSQL
 ========================
-Last updated:		Thu Jan 11 16:06:57 EST 2001
+Last updated:		Fri Jan 12 00:22:50 EST 2001
 
 Current maintainer:	Bruce Momjian (pgman@candle.pha.pa.us)
 
@@ -200,6 +200,7 @@ REFERENTIAL INTEGRITY
 * Add deferred trigger queue file (Jan)
 * Allow oid to act as a foreign key
 * Implement dirty reads and use them in RI triggers
+* Enforce referential integrity for system tables
 
 EXOTIC FEATURES