Feature cuke describing desired behavior.

It seems this never worked, as I was not able to get any combinations to
pass on Travis CI; despite what I said and others reported in the
original issue: https://github.com/rspec/rspec-rails/issues/998

According to the rails routing docs, if you want to redirect to another
action for the same controller, you need to use `:action`.
Include extra cukes for routing helpers in example

As a safe guard to prevent stomping on available helpers, add two new
cukes to verify they are available in the example.
Copy `with_routing` to make url helpers available.

- Routing in controllers appears on the surface to only allow a single
  instance of `RouteSet`. However, internally, it does a complex
  delegation and hierarchy dance to support mixing in additional routes!

  - See: https://github.com/rails/rails/blob/f88d087f15/actionpack/lib/action_dispatch/routing/route_set.rb#L417
  - See: https://github.com/rails/rails/blob/f88d087f15/actionpack/lib/action_dispatch/routing/url_for.rb#L150
  - See: https://github.com/rails/rails/blob/f88d087f15/actionpack/lib/abstract_controller/url_for.rb#L12

- Unlike the `with_routing` code, we are not re-setting the controller
  instance in the after block. That is because for the lifetime of this
  instance, the controller should use the updated routes.

- Fixes #998