Fixed error when using different implementation of IResponse

Fixed error during exception handling when using different implementation of IResponse.

In process excpetion code access property warnOnBuffer which is not part of IResponse interface but only of it's specific implementation. Resolved by adding check for type.
I open the entire `Application.php`. You need to use `instanceof Nette\Http\Response` or add the `use Nette\Http` + update  every usage of class in `Http` namespace, otherwise you break consistency.