[HttpFoundation] do not use server variable PATH_INFO 

because it is already decoded (see http://www.ietf.org/rfc/rfc3875) and thus symfony is fragile to double encoding of the path. This is not really a security issue (in contrast to a [previous problem](http://symfony.com/blog/security-release-symfony-2-0-20-and-2-1-5-released)) but when using the apacherequest, one could access pages with double encoded characters although the path should not match.

BC break: no
tests pass: yes