less verbosity -- avoid slightly odd tracing information on warning channel;

--- a/src/HOL/Tools/arith_data.ML	Thu Jan 13 18:00:13 2011 +0100
+++ b/src/HOL/Tools/arith_data.ML	Thu Jan 13 20:54:07 2011 +0100
@@ -54,9 +54,7 @@
 fun gen_arith_tac verbose ctxt =
   let
     val tactics = Arith_Tactics.get (ProofContext.theory_of ctxt);
-    fun invoke (_, (name, tac)) k st =
-     (if verbose then warning ("Trying " ^ name ^ "...") else ();
-      tac verbose ctxt k st);
+    fun invoke (_, (name, tac)) k st = tac verbose ctxt k st;
   in FIRST' (map invoke (rev tactics)) end;
 
 val arith_tac = gen_arith_tac false;