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

ErrorHandler.php

@@ -352,10 +352,12 @@ private function reRegister($prev)
     /**
      * Handles errors by filtering then logging them according to the configured bit fields.
      *
-     * @param int    $type    One of the E_* constants
+     * @param int    $type      One of the E_* constants
+     * @param string $message
      * @param string $file
      * @param int    $line
      * @param array  $context
+     * @param array  $backtrace
      *
      * @return bool Returns false when no handling happens so that the PHP engine can handle the error itself
      *