React fix

Now that weak references are properly implemented by Js_of_ocaml, we need
to make sure that signals and events do not get garbage collected too
early.

template.distillery/demo_notif.eliom

@@ -2,7 +2,6 @@
 (* This file was generated by Ocsigen Start.
    Feel free to use it, modify it, and redistribute it as you wish. *)
 (* Notification demo *)
-
 open Js_of_ocaml_lwt]
 
 (* Service for this demo *)
@@ -54,12 +53,13 @@ let%server () =
       let e : (unit * string) Eliom_react.Down.t = Notif.client_ev () in
       ignore
         [%client
-          (ignore
-           @@ React.E.map
-                (fun (_, msg) ->
-                  (* Eliom_lib.alert "%s" msg *)
-                  Os_msg.msg ~level:`Msg (Printf.sprintf "%s" msg))
-                ~%e
+          (Eliom_lib.Dom_reference.retain Js_of_ocaml.Dom_html.window
+             ~keep:
+               (React.E.map
+                  (fun (_, msg) ->
+                    (* Eliom_lib.alert "%s" msg *)
+                    Os_msg.msg ~level:`Msg (Printf.sprintf "%s" msg))
+                  ~%e)
             : unit)];
       Lwt.return_unit)