Bug 148755 Add tthe status to the ActivityStackEvent.
If the the event rollback, the ActivityStackEvent status should be ROLL_BACK.
model/org.eclipse.birt.report.model/src/org/eclipse/birt/report/model/activity/ActivityStack.java
* {@link #removeListener}methods add and remove listeners. The listener class
 * will be notified when {@link #execute(IActivityRecord)},{@link #commit()},
 * {@link #undo()}, or {@link #redo()}is called. The event
 * <code>ActivityStackEvent</code> contains the cause of the activity stack
 * change.
 * 
 */
public class ActivityStack implements CommandStack
{
	/**
	 * The default stack size limit.
	 */
	public static final int DEFAULT_STACK_LIMIT = 500;
	/**
	 * The undo stack. Entries are of type ActivityRecord.
	 */
	private Stack undoStack = new Stack( );
	/**
	 * The redo stack. Entries are of type ActivityRecord.
	 */
	private Stack redoStack = new Stack( );
	/**
	 * The active transaction stack. Entries are of type CompoundCommand.
	 */
	private Stack transStack = new Stack( );
	/**
	 * The stack size limit. The limit applies to the undo stack. Since the redo
	 * stack holds items from the undo stack, by definition the redo stack can
	 * never hold more items than the undo stack once held.
	 */