Merge branch '3.4' into 4.0

* 3.4:
  [HttpFoundation] update phpdoc of FlashBagInterface::add()
  [ProxyManagerBridge] Fix support of private services (bis)
  bug #27701 [SecurityBundle] Dont throw if "security.http_utils" is not found (nicolas-grekas)
  [Form] relax fixtures for forward compat
  [Validator] Fix the namespace of RegexTest
  [Lock] fix locale dependent test case

Author: nicolas-grekas

Tests/Constraints/RegexTest.php

@@ -9,7 +9,7 @@
  * file that was distributed with this source code.
  */
 
-namespace Constraints;
+namespace Symfony\Component\Validator\Tests\Constraints;
 
 use PHPUnit\Framework\TestCase;
 use Symfony\Component\Validator\Constraints\Regex;