Update: fix a clash between Stdlib and List compare (since ocaml 4.12)

lib/lutin/poly_draw.ml

@@ -614,7 +614,7 @@ let (_draw_point_cheap2 : point list -> point) =
        The result is not too bad, but not perfect...
     *)
     let ul0 = List.map (fun _ -> Random.float 1.0) (List.tl zl) in
-    let ul = List.sort compare ul0 in
+    let ul = List.sort Stdlib.compare ul0 in
     let (u_last, sl0) =
       List.fold_left
 	     (fun (u', l) u -> (u, (u -. u')::l))