handle both TVars and TFrees -- necessary for 'wrap_free_constructors'

--- a/src/HOL/BNF/Tools/bnf_ctr_sugar.ML	Mon Aug 12 09:38:42 2013 +0200
+++ b/src/HOL/BNF/Tools/bnf_ctr_sugar.ML	Mon Aug 12 09:51:00 2013 +0200
@@ -202,9 +202,13 @@
       Binding.qualify mandatory data_b_name o
       (rep_compat ? Binding.qualify false rep_compat_prefix);
 
+    fun tfree_name_of (TFree (s, _)) = s
+      | tfree_name_of (TVar ((s, _), _)) = s
+      | tfree_name_of (Type (s, _)) = Long_Name.base_name s;
+
     val (As, B) =
       no_defs_lthy
-      |> variant_tfrees (map (fst o fst o dest_TVar) As0)
+      |> variant_tfrees (map tfree_name_of As0)
       ||> the_single o fst o mk_TFrees 1;
 
     val dataT = Type (dataT_name, As);