Rationalize railtie dependencies: AC uses AV; AR uses AMo; and Rails always uses AS.

actionmailer/lib/action_mailer/railtie.rb

@@ -22,4 +22,4 @@ module ActionMailer
       ActionMailer::Base.send(:include, ActionController::UrlFor) if defined?(ActionController)
     end
   end
-end
+end

actionpack/lib/action_controller/railtie.rb

@@ -1,5 +1,6 @@
 require "action_controller"
 require "rails"
+require "action_view/railtie"
 
 module ActionController
   class Railtie < Rails::Railtie

activerecord/lib/active_record/railtie.rb

@@ -1,10 +1,12 @@
+require "active_record"
+require "rails"
+require "active_model/railtie"
+
 # For now, action_controller must always be present with
 # rails, so let's make sure that it gets required before
 # here. This is needed for correctly setting up the middleware.
 # In the future, this might become an optional require.
-require "active_record"
 require "action_controller/railtie"
-require "rails"
 
 module ActiveRecord
   class Railtie < Rails::Railtie

railties/lib/rails/all.rb

@@ -1,11 +1,8 @@
 require "rails"
 
 %w(
-  active_support
-  active_model
   active_record
   action_controller
-  action_view
   action_mailer
   active_resource
   rails/test_unit
@@ -14,4 +11,4 @@ require "rails"
     require "#{framework}/railtie"
   rescue LoadError
   end
-end
+end