boot.rb

# add this to the bottom of config/boot.rb, before the line `Rails.boot!`

class Rails::Boot
  def run
    load_initializer

    Rails::Initializer.class_eval do
      def load_gems
        @bundler_loaded ||= Bundler.require :default, Rails.env
      end
    end

    Rails::Initializer.run(:set_load_path)
  end
end

Gemfile

# include at least one source and the rails gem
source :gemcutter
gem 'rails', '~> 2.3.5', :require => nil
gem 'sqlite3-ruby', :require => 'sqlite3'

# Devise 1.0.2 is not a valid gem plugin for Rails, so use git until 1.0.3
# gem 'devise', :git => 'git://github.com/plataformatec/devise.git', :ref => 'v1.0'

group :development do
  # bundler requires these gems in development
  gem 'rails-footnotes'
end

group :test do
  # bundler requires these gems while running tests
  gem 'rspec'
end

preinitializer.rb

begin
  require "rubygems"
  require "bundler"

  if Gem::Version.new(Bundler::VERSION) <= Gem::Version.new("0.9.20")
    raise RuntimeError, "Your bundler version is too old." +
     "Run `gem install bundler` to upgrade."
  end

  # Set up load paths for all bundled gems
  ENV["BUNDLE_GEMFILE"] = File.expand_path("../../Gemfile", __FILE__)
  Bundler.setup
end