Signed-off-by: NYehuda Katz <wycats@Yehuda-Katz.local>

adding any to the load path more than once.

  * A new module (ActiveSupport::Autoload) is provide that extends
    autoloading with new behavior.
  * All autoloads in modules that have extended ActiveSupport::Autoload
    will be eagerly required in threadsafe environments
  * Autoloads can optionally leave off the path if the path is the same
    as full_constant_name.underscore
  * It is possible to specify that a group of autoloads live under an
    additional path. For instance, all of ActionDispatch's middlewares
    are ActionDispatch::MiddlewareName, but they live under 
    "action_dispatch/middlewares/middleware_name"
  * It is possible to specify that a group of autoloads are all found
    at the same path. For instance, a number of exceptions might all
    be declared there.
  * One consequence of this is that testing-related constants are not
    autoloaded. To get the testing helpers for a given component,
    require "component_name/test_case". For instance, "action_controller/test_case".
  * test_help.rb, which is automatically required by a Rails application's
    test helper, requires the test_case.rb for all active components, so
    this change will not be disruptive in existing or new applications.

  * This initial implementation is a bit hackish, but it uses a normal middleware API
    so it's future-proof when we improve the internals.

Renamed ActionController::Renderer to ActionController::Responder and ActionController::MimeResponds::Responder to ActionController::MimeResponds::Collector.

This commit breaks all exception catching plugins like ExceptionNotifier. These plugins should be rewritten as middleware instead overriding Controller#rescue_action_in_public.