Merge branch '2.8' into 3.3

* 2.8:
  [FrameworkBundle] Fix visibility of a test helper
  [link] clear the cache after linking
  [link] Prevent warnings when running link with 2.7
  [Validator] ExpressionValidator should use OBJECT_TO_STRING to allow value in message

Author: nicolas-grekas

Tests/Controller/RedirectControllerTest.php

@@ -290,7 +290,7 @@ private function createRedirectController($httpPort = null, $httpsPort = null)
         return $controller;
     }
 
-    public function assertRedirectUrl(Response $returnResponse, $expectedUrl)
+    private function assertRedirectUrl(Response $returnResponse, $expectedUrl)
     {
         $this->assertTrue($returnResponse->isRedirect($expectedUrl), "Expected: $expectedUrl\nGot:      ".$returnResponse->headers->get('Location'));
     }