tuned quickcheck's response

--- a/src/HOL/Tools/Quickcheck/quickcheck_common.ML	Fri Dec 09 11:31:13 2011 +0100
+++ b/src/HOL/Tools/Quickcheck/quickcheck_common.ML	Fri Dec 09 12:21:01 2011 +0100
@@ -113,6 +113,7 @@
         !current_result)
     | SOME test_fun =>
       let
+        val _ = Quickcheck.message ctxt ("Testing conjecture with with Quickcheck-" ^ name ^ "...");
         val (response, exec_time) =
           cpu_time "quickcheck execution" (fn () => with_size test_fun genuine_only 1)
         val _ = Quickcheck.add_response names eval_terms response current_result