cannot load railtie after upgrade to rails 4 per ruby.railstutorial.org

OS is Ubuntu 12.04, 64 bit.

New to rails. Relatively new to Ruby. Following the ruby.railstutorial.org tutorial, chapter 3.

The tutorial has been updated to use ruby 2.0.0 and Rails 4.0.0.rc1. Previously the gemfile was specifying Rails 3.2.13 and not specifying Ruby version. After moving to the latest Gemfile in the tutorial, ruby 2.0.0 and Rails 4.0.0.rc1, I'm getting the following error when running rails commands. Example here is rails server

    user@machine:~/bin/railslearn/sample_app$ rails server
/home/paul/bin/railslearn/sample_app/config/application.rb:7:in `require': cannot load such file -- active_resource/railtie (LoadError)
    from /home/paul/bin/railslearn/sample_app/config/application.rb:7:in `<top (required)>'
    from /home/paul/.rvm/gems/ruby-2.0.0-p195@railstutorial_rails_4_0/gems/railties-4.0.0.rc1/lib/rails/commands.rb:78:in `require'
    from /home/paul/.rvm/gems/ruby-2.0.0-p195@railstutorial_rails_4_0/gems/railties-4.0.0.rc1/lib/rails/commands.rb:78:in `block in <top (required)>'
    from /home/paul/.rvm/gems/ruby-2.0.0-p195@railstutorial_rails_4_0/gems/railties-4.0.0.rc1/lib/rails/commands.rb:75:in `tap'
    from /home/paul/.rvm/gems/ruby-2.0.0-p195@railstutorial_rails_4_0/gems/railties-4.0.0.rc1/lib/rails/commands.rb:75:in `<top (required)>'
    from script/rails:6:in `require'
    from script/rails:6:in `<main>'

I did get some ideas from Rails: Could not find railties, outlined below, but haven't yet found a fix.

Here's the details.

Yesterday (in my browser) the Gemfile for Chapter 3 was as follows. Everything worked fine.

$ cat Gemfile
source 'https://rubygems.org'

gem 'rails', '3.2.13'
gem 'bootstrap-sass', '2.1'
gem 'bcrypt-ruby', '3.0.1'
gem 'faker', '1.0.1'
gem 'will_paginate', '3.0.3'
gem 'bootstrap-will_paginate', '0.0.6'
gem '