Merge branch '3.4' into 4.4

* 3.4:
  [VarDumper] fix side-effect by not using mt_rand()

src/Symfony/Component/VarDumper/Cloner/VarCloner.php

@@ -46,7 +46,7 @@ class VarCloner extends AbstractCloner
                                         // or null if the original value is used directly
 
         if (!$gid = self::$gid) {
-            $gid = self::$gid = uniqid(mt_rand(), true); // Unique string used to detect the special $GLOBALS variable
+            $gid = self::$gid = md5(random_bytes(6)); // Unique string used to detect the special $GLOBALS variable
         }
         $arrayStub = new Stub();
         $arrayStub->type = Stub::TYPE_ARRAY;