Ensure that our load hooks really for real run after Rails

While changing the code to be in an `on_load` hook fixed some of the issues
with load hook order, it didn't catch all of them. Rails runs its hooks in
initializers, meaning they'll be defined after our own hooks which are not in
an initializer.

Fixes #24

lib/rails-controller-testing.rb

@@ -4,15 +4,19 @@
 require 'rails/controller/testing/template_assertions'
 require 'rails/controller/testing/version'
 
-ActiveSupport.on_load(:action_controller) do
-  ActionController::TestCase.include Rails::Controller::Testing::TestProcess
-  ActionController::TestCase.include Rails::Controller::Testing::TemplateAssertions
+class Rails::Controller::Testing::Railtie < Rails::Railtie
+  initializer "rails_controller_testing" do
+    ActiveSupport.on_load(:action_controller) do
+      ActionController::TestCase.include Rails::Controller::Testing::TestProcess
+      ActionController::TestCase.include Rails::Controller::Testing::TemplateAssertions
 
-  ActionDispatch::IntegrationTest.include Rails::Controller::Testing::TemplateAssertions
-  ActionDispatch::IntegrationTest.include Rails::Controller::Testing::Integration
-  ActionDispatch::IntegrationTest.include Rails::Controller::Testing::TestProcess
-end
+      ActionDispatch::IntegrationTest.include Rails::Controller::Testing::TemplateAssertions
+      ActionDispatch::IntegrationTest.include Rails::Controller::Testing::Integration
+      ActionDispatch::IntegrationTest.include Rails::Controller::Testing::TestProcess
+    end
 
-ActiveSupport.on_load(:action_view) do
-  ActionView::TestCase.include Rails::Controller::Testing::TemplateAssertions
+    ActiveSupport.on_load(:action_view) do
+      ActionView::TestCase.include Rails::Controller::Testing::TemplateAssertions
+    end
+  end
 end