[JENKINS-3969] Replaced all gif images with corresponding png images.

changelog.html

@@ -70,6 +70,9 @@ Upcoming changes</a>
   <li class=rfe>
     Provide more information to <tt>QueueTaskDispatcher</tt>
     (<a href="https://groups.google.com/d/topic/jenkinsci-dev/H1o_essBS_A/discussion">thread</a>)
+  <li class=rfe>
+    Replaced all gif images with png images (transparency support).
+    (<a href="http://issues.jenkins-ci.org/browse/JENKINS-3969">issue 3969</a>)
 </ul>
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