Allow Standard Response Mechanisms To Include Headers

It would be useful to allow for methods like ok to include headers. For example:

class Foos < Application
  def show
    @foo = Foo[:id => params[:id]]
    ok @foo, 'Content-Language' => @foo[:language]
  end
end

Variations of this would be fine. It should also work for the other responders (suggested in another ticket; status and error and the like).