simplified equality on pairs of types;

--- a/src/Tools/subtyping.ML	Wed Dec 01 11:01:20 2010 +0100
+++ b/src/Tools/subtyping.ML	Wed Dec 01 11:06:01 2010 +0100
@@ -397,7 +397,7 @@
         val pairs = (last, hd nodes) :: (but_last ~~ tl nodes);
       in
         map_filter
-          (fn (TU, pack) => if member (eq_pair (op =) (op =)) pairs TU then SOME pack else NONE) 
+          (fn (TU, pack) => if member (op =) pairs TU then SOME pack else NONE)
           cs'
       end;