[HttpFoundation] add missing support for the new output API in PHP 5.4...

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets |
| License       | MIT
| Doc PR        |

As of PHP 5.4, the new output API has been introduced:

* https://github.com/php/php-src/blob/master/README.NEW-OUTPUT-API
* https://github.com/php/php-src/commit/11d24c1593d6617f73d3f290617bd8994182f4dc
* https://bugs.php.net/bug.php?id=64977