bschussek made significant changes to the EventDispatcher implementation
to make it similar to the one Doctrine2 uses.

most significant change in this commit is that returning something from
an error handler will now stop propagation.

Fixed request not being saved in Framework->request attribute when no matching routes are found for a certaing request URI

the update to the latest Symfony2 replaces Response::setRedirect with a new RedirectResponse class. it also changed some internals of the HttpKernel.

other core.view listeners may want to handle the return value too. if all else fails, convert it to a string and then to a response object.