Small updates based on jglick comments

core/src/main/java/hudson/ExtensionList.java

@@ -84,7 +84,7 @@ public class ExtensionList<T> extends AbstractList<T> {
     @CopyOnWrite
     private volatile List<ExtensionComponent<T>> extensions;
 
-    private List<ExtensionListListener> listeners = new CopyOnWriteArrayList<ExtensionListListener>();
+    private final List<ExtensionListListener> listeners = new CopyOnWriteArrayList<ExtensionListListener>();
 
     /**
      * Place to store manually registered instances with the per-Hudson scope.

core/src/main/java/hudson/ExtensionListListener.java

@@ -27,6 +27,7 @@ package hudson;
  * {@link ExtensionList} listener.
  *
  * @author <a href="mailto:tom.fennelly@gmail.com">tom.fennelly@gmail.com</a>
+ * @since TODO
  */
 public abstract class ExtensionListListener {