* 2.0:
[Bundle] [FrameworkBundle] fixed indentation in esi.xml services file.
[TwigBundle] There is no CSS visibility of display, should be visible instead
[DependencyInjection] fixed a bug where the strict flag on references were lost (closes#6607)
[HttpFoundation] Check if required shell functions for `FileBinaryMimeTypeGuesser` are not disabled
[CssSelector] added css selector with empty string
[HttpFoundation] Docblock for Request::isXmlHttpRequest() now points to Wikipedia
[DependencyInjection] refactored code to avoid logic duplication
Conflicts:
src/Symfony/Bundle/FrameworkBundle/Resources/config/esi.xml
src/Symfony/Component/DependencyInjection/Dumper/PhpDumper.php
src/Symfony/Component/HttpFoundation/File/MimeType/FileBinaryMimeTypeGuesser.php
