Bug 249574 [Contributions] ExternalActionManager.addPropertyChangeListener() doesn't register the ListenerList
bundles/org.eclipse.jface/src/org/eclipse/jface/action/ExternalActionManager.java
/**
	 * Constructs a new instance of <code>ExternalActionManager</code>.
	 */
	private ExternalActionManager() {
		
	}
	/**
	 * An accessor for the current call back.
	 * 
	 * @return The current callback mechanism being used. This is the callback
	 *         that should be queried for extra information about actions and
	 *         action contribution items. This value may be <code>null</code>
	 *         if there is no extra information.
	 */
	public ICallback getCallback() {
		return callback;
	}
	/**
	 * A mutator for the current call back
	 * 
	 * @param callbackToUse
	 *            The new callback mechanism to use; this value may be
	 *            <code>null</code> if the default is acceptable (i.e., no
	 *            extra information will provided to actions).
	 */
	public void setCallback(ICallback callbackToUse) {
		callback = callbackToUse;
	}
}