proper escaping in file name

--- a/src/HOL/TPTP/mash_eval.ML	Sat Dec 15 18:26:37 2012 +0100
+++ b/src/HOL/TPTP/mash_eval.ML	Sat Dec 15 18:48:58 2012 +0100
@@ -90,7 +90,8 @@
         fun set_file_name heading (SOME dir) =
             let
               val prob_prefix =
-                "goal_" ^ string_of_int j ^ "__" ^ name ^ "__" ^ heading
+                "goal_" ^ string_of_int j ^ "__" ^ escape_meta name ^ "__" ^
+                heading
             in
               Config.put Sledgehammer_Provers.dest_dir dir
               #> Config.put Sledgehammer_Provers.problem_prefix