Merge branch '3.1'

* 3.1:
  [FrameworkBundle] Check for class existence before is_subclass_of
  Update GroupSequence.php
  Code enhancement and cleanup
  [Form] Fix transformer tests after the ICU update
  [DI] Add anti-regression test
  Revert "minor #19689 [DI] Cleanup array_key_exists (ro0NL)"
  bumped Symfony version to 3.1.5
  updated VERSION for 3.1.4
  updated CHANGELOG for 3.1.4
  bumped Symfony version to 2.8.11
  updated VERSION for 2.8.10
  updated CHANGELOG for 2.8.10
  [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

Command/DebugCommand.php

@@ -139,7 +139,6 @@ private function getMetadata($type, $entity)
             return;
         }
         if ($type === 'functions' || $type === 'filters') {
-            $args = array();
             $cb = $entity->getCallable();
             if (is_null($cb)) {
                 return;