Merge branch '2.7' into 2.8

* 2.7:
  [FrameworkBundle] Check for class existence before is_subclass_of
  Update GroupSequence.php
  Code enhancement and cleanup
  [DI] Add anti-regression test
  Revert "minor #19689 [DI] Cleanup array_key_exists (ro0NL)"
  [BrowserKit] Fix cookie expiration on 32 bit systems
  bumped Symfony version to 2.7.18
  updated VERSION for 2.7.17
  update CONTRIBUTORS for 2.7.17
  updated CHANGELOG for 2.7.17
  Update misleading comment about RFC4627

Author: nicolas-grekas

Constraints/GroupSequence.php

@@ -19,7 +19,7 @@
  * When validating a group sequence, each group will only be validated if all
  * of the previous groups in the sequence succeeded. For example:
  *
- *     $validator->validate($address, null, new GroupSequence('Basic', 'Strict'));
+ *     $validator->validate($address, null, new GroupSequence(array('Basic', 'Strict')));
  *
  * In the first step, all constraints that belong to the group "Basic" will be
  * validated. If none of the constraints fail, the validator will then validate

Tests/Validator/Abstract2Dot5ApiTest.php

@@ -40,6 +40,7 @@ abstract class Abstract2Dot5ApiTest extends AbstractValidatorTest
 
     /**
      * @param MetadataFactoryInterface $metadataFactory
+     * @param array                    $objectInitializers
      *
      * @return ValidatorInterface
      */