fixed soundness bug / type error in handling of unpolarized (co)inductive predicates in Nitpick

--- a/src/HOL/Tools/Nitpick/nitpick_hol.ML	Tue Nov 24 10:31:01 2009 +0100
+++ b/src/HOL/Tools/Nitpick/nitpick_hol.ML	Tue Nov 24 10:33:02 2009 +0100
@@ -2471,7 +2471,7 @@
                        list_comb (f (),
                                   map Bound (length trunk_arg_Ts - 1 downto 0))
                    in
-                     List.foldl absdummy
+                     List.foldr absdummy
                                 (Const (set_oper, [set_T, set_T] ---> set_T)
                                         $ app pos $ app neg) trunk_arg_Ts
                    end