Merge branch '2.8' into 3.2

* 2.8:
  Using FQ name for PHP_VERSION_ID
  [Form] Fix \IntlDateFormatter timezone parameter usage to bypass PHP bug #66323
  Harden the debugging of Twig filters and functions
  bumped Symfony version to 2.8.22
  updated VERSION for 2.8.21
  updated CHANGELOG for 2.8.21
  bumped Symfony version to 2.7.29
  updated VERSION for 2.7.28
  update CONTRIBUTORS for 2.7.28
  updated CHANGELOG for 2.7.28

Author: fabpot

Tests/DateFormatter/AbstractIntlDateFormatterTest.php

@@ -435,7 +435,7 @@ public function testFormatWithDateTimeZoneGmt()
 
     public function testFormatWithDateTimeZoneGmtOffset()
     {
-        if (defined('HHVM_VERSION_ID') || PHP_VERSION_ID <= 50509) {
+        if (defined('HHVM_VERSION_ID') || \PHP_VERSION_ID <= 50509) {
             $this->markTestSkipped('DateTimeZone GMT offsets are supported since 5.5.10. See https://github.com/facebook/hhvm/issues/5875 for HHVM.');
         }