title: What does #self.included(base) do in Ruby on Rails' Restful Authentication?
body: <p>I thought we would do</p>
  
  <pre><code>helper_method :current_user, :logged_in?, :authorized?
  </code></pre>
  
  <p>to make these controller methods available for use as helper methods in views. But in Restful Authentication's <code>lib/authenticated_system.rb</code>, I see:</p>
  
  <pre><code># Inclusion hook to make #current_user and #logged_in?
  # available as ActionView helper methods.
  def self.included(base)
    base.send :helper_method, :current_user, :logged_in?, :authorized? if base.respond_to? :helper_method
  end
  </code></pre>
  
  <p>Why is it done this way instead of that single line? Also, I don't see <code>included</code> being called anywhere.</p>