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

Tests/DebugClassLoaderTest.php

@@ -61,7 +61,7 @@ class DebugClassLoaderTest extends TestCase
 
     public function testUnsilencing()
     {
-        if (PHP_VERSION_ID >= 70000) {
+        if (\PHP_VERSION_ID >= 70000) {
             $this->markTestSkipped('PHP7 throws exceptions, unsilencing is not required anymore.');
         }
         if (defined('HHVM_VERSION')) {
@@ -109,7 +109,7 @@ class DebugClassLoaderTest extends TestCase
         } catch (\ErrorException $exception) {
             // if an exception is thrown, the test passed
             $this->assertStringStartsWith(__FILE__, $exception->getFile());
-            if (PHP_VERSION_ID < 70000) {
+            if (\PHP_VERSION_ID < 70000) {
                 $this->assertRegExp('/^Runtime Notice: Declaration/', $exception->getMessage());
                 $this->assertEquals(E_STRICT, $exception->getSeverity());
             } else {
@@ -245,7 +245,7 @@ class DebugClassLoaderTest extends TestCase
 
     public function testReservedForPhp7()
     {
-        if (PHP_VERSION_ID >= 70000) {
+        if (\PHP_VERSION_ID >= 70000) {
             $this->markTestSkipped('PHP7 already prevents using reserved names.');
         }