Can't alter the middleware stack in environment.rb

On edge (current as of 25 July, and dating back to 25 June), you can't manipulate the middleware stack by adding code like the following to environment.rb:

Rails::Initializer.run do |config|
config.middleware.use MyCustomMiddleware end

This raises the following error:

..../config/../vendor/rails/railties/lib/rails/configuration.rb:111:in middleware':NameError: uninitialized constant Rails::Configuration::ActionController

It looks like this was caused by the removal of a require 'action_controller' from within the middleware method.