Partial revert of commit #7fae0aa4 removing...

Partial revert of commit #7fae0aa4 removing action_dispatch.prepare_dispatcher per commit #48bf667a

See line note:
http://github.com/rails/rails/commit/7fae0aa4ac116bcbf522a9a4f19972c653d366fa#commitcomment-145148

actionpack/lib/action_dispatch/railtie.rb

@@ -10,11 +10,6 @@ class Railtie < Rails::Railtie
     config.action_dispatch.best_standards_support = true
     config.action_dispatch.tld_length = 1
 
-    # Prepare dispatcher callbacks and run 'prepare' callbacks
-    initializer "action_dispatch.prepare_dispatcher" do |app|
-      ActionDispatch::Callbacks.to_prepare { app.routes_reloader.execute_if_updated }
-    end
-
     initializer "action_dispatch.configure" do |app|
       ActionDispatch::Http::URL.tld_length = app.config.action_dispatch.tld_length
     end