Merge branch '2.7' into 2.8

* 2.7:
  [HttpFoundation] Fix transient test
  [HttpFoundation] Add a dependency on the mbstring polyfill
  [2.7] update readme files for new components
  add readme files where missing
  fix lowest TwigBridge deps versions
  [EventDispatcher] fix syntax error
  Don't use reflections when possible
  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
  [Process] Fix memory issue when using large input streams
  Use constant instead of function call.
  fixed test name
  automatically generate safe fallback filename
  [Console] default to stderr in the console helpers

Conflicts:
	composer.json
	src/Symfony/Bridge/PhpUnit/README.md
	src/Symfony/Bridge/Twig/composer.json
	src/Symfony/Component/Console/Helper/DialogHelper.php
	src/Symfony/Component/Debug/DebugClassLoader.php
	src/Symfony/Component/HttpFoundation/composer.json
	src/Symfony/Component/Security/Acl/README.md
	src/Symfony/Component/Security/Core/README.md
	src/Symfony/Component/Security/Csrf/README.md
	src/Symfony/Component/Security/Http/README.md

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