Merge branch '2.3' into 2.7

* 2.3:
  [HttpFoundation] Fix transient test
  [HttpFoundation] Add a dependency on the mbstring polyfill
  add readme files where missing
  Don't use reflections when possible
  [Form] Update form tests after the ICU data update
  [Intl] Update tests and the number formatter to match behaviour of the intl extension
  [Intl] Update the ICU data to version 55
  [Intl] Fix the update-data.php script in preparation for ICU 5.5
  Use constant instead of function call.
  fixed test name
  automatically generate safe fallback filename

Conflicts:
	src/Symfony/Component/Debug/Debug.php
	src/Symfony/Component/HttpFoundation/composer.json
	src/Symfony/Component/Serializer/Tests/Normalizer/GetSetMethodNormalizerTest.php

Author: nicolas-grekas

Tests/Normalizer/GetSetMethodNormalizerTest.php

@@ -651,6 +651,11 @@ public static function setStaticObject($object)
     {
         self::$staticObject = $object;
     }
+
+    protected function getPrivate()
+    {
+        throw new \RuntimeException('Dummy::getPrivate() should not be called');        
+    }
 }
 
 class GetConstructorDummy