title: Where is asset_host rails 3?
body: <p>What happened to asset_host in rails 3?
  Earlier I can put following code into development.rb and get all assets not present on development:</p>
  
  <pre><code>ActionController::Base.asset_host = proc do |source, request|
    unless File.exist?(File.join(RAILS_ROOT, 'public', source.sub(/\?\d+$/, '')))
      'http://example.com'
    end
  end
  </code></pre>
  
  <p>But in rails 3 there is no such method and google does not help me.</p>