fix dependencies on HttpFoundation component

| Q             | A
| ------------- | ---
| Bug fix?      | yes
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | #11636
| License       | MIT
| Doc PR        | 

The ``closeOutputBuffers()`` method was added to the ``Response`` class of the HttpFoundation in Symfony 2.5. Therefore, parts that are calling this method must depend on ``symfony/http-foundation`` 2.5 or higher.
``Response::closeOutputBuffers()`` is called in [the ExceptionController](https://github.com/symfony/symfony/blob/2.5/src/Symfony/Bundle/TwigBundle/Controller/ExceptionController.php#L77). I don't know why the HttpFoundation component isn't required here. But we then need to increase the HttpKernel dependency to indirectly receive the needed version of the HttpFoundation.

I would be more happy with requiring the HttpFoundation component here explicitly. If you agree, I'll add it and revert the change to the HttpKernel dependency.