Change the Forget operator so that it uses the tallying and not the subtyping.

For instance :
  let f : Int -> Int = (fun ('a -> 'a) x -> x)
is now accepted.

typing/typer.ml

@@ -1212,10 +1212,13 @@ let rec type_check env e constr precise =
 
 and type_check' loc env ed constr precise = match ed with
   | Forget (e,t) ->
-    let t = Types.descr t in
-    ignore (type_check env e t false);
-    (ed,verify loc t constr)
-
+     let t = Types.descr t in
+     let te = type_check env e Types.any true in
+     let delta = Var.Set.cup (Types.all_vars t) env.delta in
+     if Type_tallying.is_squaresubtype delta te t then
+       (ed,verify loc t constr)
+     else
+       raise_loc loc (Constraint(t, te))
   | Subst (e,sl) ->
     let t = type_check env e constr precise in
     (ed,verify loc t constr)