updated changelog for release

changelog.html

@@ -54,12 +54,16 @@ Upcoming changes</a>
 
 <!-- Record your changes in the trunk here. -->
 <div id="trunk" style="display:none"><!--=TRUNK-BEGIN=-->
+<ul class=image>
+  <li class=>
+</ul>
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+<h3><a name=v1.644>What's new in 1.644</a> (2016/01/10)</h3>
 <ul class=image>
   <li class="rfe">
     API changes: Add a reusable implementation of <code>IdleOfflineCause</code> class.
     (<a href="https://github.com/jenkinsci/jenkins/commit/7e05b5032e138b5780eabc790d7cddecdc9b0b7c">commit 7e05b50</a>)
 </ul>
-</div><!--=TRUNK-END=-->
 <h3><a name=v1.643>What's new in 1.643</a> (2015/12/20)</h3>
 <ul class=image>
   <li class="bug">