Kohana::$user_agent moved to the request helper and is protected, so

instead set the user agent into $_SERVER.

modules/gallery/hooks/init_gallery.php

@@ -42,5 +42,5 @@
 }
 
 if ($user_agent = $input->post("user_agent", $input->get("user_agent"))) {
-  Kohana::$user_agent = $user_agent;
+  $_SERVER["HTTP_USER_AGENT"] = $user_agent;
 }