Allow users to configure the queue for the mailers

This allow the users to do:

    config.action_mailer.queue = MyQueue.new

and

    class UsersMailer < ActionMailer::Base
      self.queue = MyQueue.new
    end

actionmailer/lib/action_mailer/base.rb

@@ -389,6 +389,8 @@ class Base < AbstractController::Base
       :parts_order  => [ "text/plain", "text/enriched", "text/html" ]
     }.freeze
 
+    class_attribute :queue
+
     class << self
       # Register one or more Observers which will be notified when mail is delivered.
       def register_observers(*observers)
@@ -486,11 +488,6 @@ def method_missing(method_name, *args)
           super
         end
       end
-
-      def queue
-        Rails.queue
-      end
-
     end
 
     attr_internal :message

actionmailer/lib/action_mailer/railtie.rb

@@ -19,6 +19,8 @@ class Railtie < Rails::Railtie
       options.javascripts_dir ||= paths["public/javascripts"].first
       options.stylesheets_dir ||= paths["public/stylesheets"].first
 
+      options.queue ||= app.queue
+
       # make sure readers methods get compiled
       options.asset_path          ||= app.config.asset_path
       options.asset_host          ||= app.config.asset_host

actionmailer/test/abstract_unit.rb

@@ -27,14 +27,7 @@
 
 FIXTURE_LOAD_PATH = File.expand_path('fixtures', File.dirname(__FILE__))
 ActionMailer::Base.view_paths = FIXTURE_LOAD_PATH
-
-class ActionMailer::Base < AbstractController::Base
-  class << self
-    def queue
-      @queue ||= Rails::Queueing::Container.new(Rails::Queueing::SynchronousQueue.new)
-    end
-  end
-end
+ActionMailer::Base.queue = Rails::Queueing::SynchronousQueue.new
 
 class MockSMTP
   def self.deliveries

railties/test/application/initializers/frameworks_test.rb

@@ -50,6 +50,23 @@ def teardown
       assert_equal "test.rails", ActionMailer::Base.default_url_options[:host]
     end
 
+    test "uses the default queue for ActionMailer" do
+      require "#{app_path}/config/environment"
+      assert_kind_of Rails::Queueing::Container, ActionMailer::Base.queue
+    end
+
+    test "allows me to configure queue for ActionMailer" do
+      app_file "config/environments/development.rb", <<-RUBY
+        AppTemplate::Application.configure do
+          Rails.queue[:mailer] = Rails::Queueing::TestQueue.new
+          config.action_mailer.queue = Rails.queue[:mailer]
+        end
+      RUBY
+
+      require "#{app_path}/config/environment"
+      assert_kind_of Rails::Queueing::TestQueue, ActionMailer::Base.queue
+    end
+
     test "does not include url helpers as action methods" do
       app_file "config/routes.rb", <<-RUBY
         AppTemplate::Application.routes.draw do