title: Default_url in Paperclip Broke with Asset Pipeline Upgrade
body: <p>I'm using Paperclip and have a default_url option like this for one of my attachments:</p>
  
  <pre><code>:default_url =&gt; '/images/missing_:style.png'
  </code></pre>
  
  <p>The asset pipeline obviously doesn't like this since the directories moved.  What's the best way to handle this?  I have two styles for this picture (:mini and :thumb).</p>