rails/rails — pull request #9669 by senny (2013-03-11 20:20:30+00:00)
Title: config.ru uses the effective Rack app

We used to pass the Rails::Application subclass to #run.
The Rails server then called #to_app to convert that class to the
actual Rack application.

if you surround `#run` with a call to `#map` the server no longer
convertes the class to the instance and we end up with unnecessary
delegation calls on every request.