Port to Eliom 3

This is a side-effect of using a more recent version of Lwt. Now,
we're using Debian packages from experimental.

src/helios_registration.ml

@@ -121,7 +121,7 @@ let () = Eliom_registration.Html5.register
     let service = Helios_services.perform_login () in
     let () = Eliom_registration.Redirection.register
       ~service
-      ~scope:Eliom_common.session
+      ~scope:Eliom_common.default_session_scope
       (fun () (user_name, admin_p) ->
         let user_type = "dummy" in
         Eliom_reference.set Helios_services.user
@@ -133,7 +133,7 @@ let () = Eliom_registration.Html5.register
 let () = Eliom_registration.Redirection.register
   ~service:Helios_services.logout
   (fun () () ->
-    Eliom_state.discard ~scope:Eliom_common.session () >>
+    Eliom_state.discard ~scope:Eliom_common.default_session_scope () >>
     return Helios_services.home)
 
 let () = Eliom_registration.Html5.register

src/helios_services.ml

@@ -40,7 +40,7 @@ let logout = service
 let perform_login () =
   Eliom_service.post_coservice
     ~csrf_safe:true
-    ~csrf_scope:Eliom_common.session
+    ~csrf_scope:Eliom_common.default_session_scope
     ~fallback:login
     ~post_params:Eliom_parameter.(string "username" ** bool "admin_p")
     ()
@@ -55,7 +55,7 @@ type user = {
 }
 
 let user = Eliom_reference.eref
-  ~scope:Eliom_common.session
+  ~scope:Eliom_common.default_session_scope
   (None : (bool * user) option)
 
 let uuid = Eliom_parameter.user_type