title: How to generate changelog: git log since last Hudson build?
body: <p>I'm using Phing to do post build tasks in Hudson.</p>
  
  <p>I want to generate changelog containing all commits since last successful Hudson build. But looks like neither Hudson nor Git plugin for Hudson does not provide <code>%last_build_time%</code> variable.</p>
  
  <p>This would be satisfying solution, (but how to get the time?):</p>
  
  <pre><code>git log --pretty="%s" --since="%last_build_time%"
  </code></pre>
  
  <p>The only way I see for now is extracting it from the job xml file, but I do not know if it is possible with Phing.</p>
  
  <p>How do you generate your change logs?</p>