sort cases on the proper key

--- a/src/HOL/Tools/Nitpick/nitpick_hol.ML	Mon Jun 21 13:35:10 2010 +0200
+++ b/src/HOL/Tools/Nitpick/nitpick_hol.ML	Mon Jun 21 14:07:00 2010 +0200
@@ -1523,7 +1523,7 @@
                   discriminate_value hol_ctxt x (Bound 0)))
       |> AList.group (op aconv)
       |> map (apsnd (List.foldl s_disj @{const False}))
-      |> sort (int_ord o pairself (size_of_term o fst))
+      |> sort (int_ord o pairself (size_of_term o snd))
       |> rev
   in
     if res_T = bool_T then