Merge branch '2.8' into 3.3

* 2.8:
  [Validator] added magic method __isset()  to File Constraint class
  [DI] Fix possible incorrect php-code when dumped strings contains newlines
  [Translation] minor: remove unused variable in test
  never match invalid IP addresses

Author: nicolas-grekas

Constraints/File.php

@@ -88,6 +88,15 @@ public function __get($option)
         return parent::__get($option);
     }
 
+    public function __isset($option)
+    {
+        if ('maxSize' === $option) {
+            return true;
+        }
+
+        return parent::__isset($option);
+    }
+
     private function normalizeBinaryFormat($maxSize)
     {
         $factors = array(