Update codeblocks to include missing 'RequestHandler' component inclu…

…sion

en/views/json-and-xml-views.rst

@@ -47,6 +47,8 @@ generating the response, you should use view files.  The value of ``_serialize``
 can be either a string or an array of view variables to serialize::
 
     class PostsController extends AppController {
+        public $components = array('RequestHandler');
+        
         public function index() {
             $this->set('posts', $this->paginate());
             $this->set('_serialize', array('posts'));
@@ -56,6 +58,8 @@ can be either a string or an array of view variables to serialize::
 You can also define ``_serialize`` as an array of view variables to combine::
 
     class PostsController extends AppController {
+        public $components = array('RequestHandler');
+        
         public function index() {
             // some code that created $posts and $comments
             $this->set(compact('posts', 'comments'));