add msg when user session expired at page admin

app/views/admin/items/_site_map_left_bar.html.erb

@@ -2,5 +2,14 @@
 	<%= render_node_and_children(Item.first(:conditions => {:parent_id => nil})) %>
 </ol>
 <script type="text/javascript">
+        $.ajaxSetup({
+    error: function(xhr, status, err) {
+    if (xhr.status == 401){
+    alert("<%= I18n.t('access.denied.ajax_401_error') %>");
+     window.location.href = '/';
+     }
+    }
+    });
+
 	bindTreeDragHandle();
 </script>