use try instead of handle

--- a/src/HOLCF/Tools/fixrec.ML	Thu Nov 05 11:47:00 2009 -0800
+++ b/src/HOLCF/Tools/fixrec.ML	Thu Nov 05 15:38:09 2009 -0800
@@ -391,7 +391,7 @@
         CHANGED (rtac rule i THEN asm_simp_tac ss i)
       end
   in
-    SUBGOAL (fn ti => tac ti handle _ => no_tac)
+    SUBGOAL (fn ti => the_default no_tac (try tac ti))
   end;
 
 val fixrec_simp_add : Thm.attribute =