short-paths: slight change to the penalty heuristic

Give the same penalty to ident containing double underscores as to ident
starting with an underscore.

typing/printtyp.ml

@@ -277,10 +277,21 @@ let rec normalize_type_path ?(cache=false) env p =
   with
     Not_found -> (p, Id)
 
+let penalty s =
+  if s <> "" && s.[0] = '_' then
+    10
+  else
+    try
+      for i = 0 to String.length s - 2 do
+        if s.[i] = '_' && s.[i + 1] = '_' then
+          raise Exit
+      done;
+      1
+    with Exit -> 10
+
 let rec path_size = function
     Pident id ->
-      (let s = Ident.name id in if s <> "" && s.[0] = '_' then 10 else 1),
-      -Ident.binding_time id
+      penalty (Ident.name id), -Ident.binding_time id
   | Pdot (p, _, _) ->
       let (l, b) = path_size p in (1+l, b)
   | Papply (p1, p2) ->