avoid low-level tsig operations;

--- a/src/HOL/Tools/functor.ML	Sun Mar 29 17:54:22 2015 +0200
+++ b/src/HOL/Tools/functor.ML	Sun Mar 29 18:18:52 2015 +0200
@@ -41,8 +41,9 @@
 
 (* type analysis *)
 
-fun term_with_typ ctxt T t = Envir.subst_term_types
-  (Type.typ_match (Proof_Context.tsig_of ctxt) (fastype_of t, T) Vartab.empty) t;
+fun term_with_typ ctxt T t =
+  Envir.subst_term_types
+    (Sign.typ_match (Proof_Context.theory_of ctxt) (fastype_of t, T) Vartab.empty) t;
 
 fun find_atomic ctxt T =
   let