Merge branch '2.8' into 3.3

* 2.8:
  Remove function_exists(__phpunit_run_isolated_test) checks

Author: nicolas-grekas

Tests/Fixtures/Validation/Article.php

@@ -2,9 +2,7 @@
 
 namespace Symfony\Bundle\FrameworkBundle\Tests\Fixtures\Validation;
 
-if (!function_exists('__phpunit_run_isolated_test')) {
-    class Article implements NotExistingInterface
-    {
-        public $category;
-    }
+class Article implements NotExistingInterface
+{
+    public $category;
 }