[FIXED JENKINS-8751] integrated the Guice branch.

Classes marked as @Extension are now instantiated by Guice.

changelog.html

@@ -69,6 +69,9 @@ Upcoming changes</a>
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-10851">issue 10851</a>) 
   <li class=rfe>  
     Permission check added when viewing configuration of computer set.
+  <li class='major rfe'>  
+    Jenkins internally started using Guice for loading extensions
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-8751">issue 8751</a>) 
 </ul>
 </div><!--=TRUNK-END=-->