title: How to get the full URL to an asset in Rails 3.2?
body: <p>Does Rails have a built in helper to get the url of an image in the asset pipeline?</p>
  
  <pre><code>path_to_image('image.jpg')
  </code></pre>
  
  <p>gets the relative path.</p>
  
  <pre><code>url_to_image('image.jpg')
  </code></pre>
  
  <p>doesn't seem to work.</p>
  
  <pre><code>"#{root_url}#{path_to_image('image.jpg')}"
  </code></pre>
  
  <p>is not very convenient (and gives an extra / between the root and the image path).</p>
  
  <p>Is there a built in method that I'm overlooking? Or do I need to create a helper?</p>