removed dead code and fixed CS
replaced deprecated Twig features
made the filesystem loader compatible with Twig 2.0

Without adding the exists() method, the code happens to work by chance,
just because the current implementation of Twig exits() method calls
findTemplate().

But we know that it won't be the case anymore as of Twig 2.0.
Merge branch '2.2' into 2.3

* 2.2:
  added missing support for the new output API in PHP 5.4+
  Fixed bug introduced in #8675
  made the filesystem loader compatible with Twig 2.0
  bumped Symfony version to 2.2.6
  updated VERSION for 2.2.5
  update CONTRIBUTORS for 2.2.5
  updated CHANGELOG for 2.2.5
  replaced deprecated Twig features

Conflicts:
	src/Symfony/Bridge/Twig/Extension/FormExtension.php
	src/Symfony/Bridge/Twig/Extension/RoutingExtension.php
	src/Symfony/Component/HttpKernel/Kernel.php