[HttpFoundation] Docblock for Request::isXmlHttpRequest() now points to Wikipedia
[HttpFoundation] Check if required shell functions for `FileBinaryMimeTypeGuesser` are not disabled
Merge branch '2.0' into 2.1

* 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
removed the .gitattributes files (closes #6605, reverts #5674)