title: Ruby: convert unix timestamp to date
body: <pre><code>irb&gt; dt = Time.now.utc
  =&gt; 2012-04-26 10:47:01 UTC
  
  irb&gt; dti = dt.to_i
  =&gt; 1335437221
  </code></pre>
  
  <p>Now, how to convert <code>dti</code> back to Date/Time ?</p>