This feature toggle allows us to switch the JRuby and jruby-rack versions
during the switch from Rails 2.3 to Rails 4. Changes include:

* New toggle in SystemEnvironment ("use.new.rails").
* JRuby jars checked into server/jruby_jars
  - Removed dependency from server/pom.xml.
* Changed packaging in cruise-modules.rb to include all 4 JRuby jars.
* Created new module development-server-new-jruby
  - Its pom.xml has a dependency on new JRuby, for dev server.
* development-server/pom.xml has old JRuby dependency added.
  - Allows people to continue to use their dev server setup with old Rails.
* Changes in GoServer.java to switch JRuby versions.
  - Just like addons, adds the correct JRuby jars to web app classpath.
  - Switches rails.root to /WEB-INF/rails.new for new JRuby.
* Comment rails.root which was hard-coded in web.xml.