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
{
		return redoStack.isEmpty( ) ? null : (ActivityRecord) redoStack.peek( );
	}
	/**
	 * Peeks at the top of the undo stack.
	 * 
	 * @return The record at the top of the undo stack, or null if there is no
	 *         such record.
	 */
	public IActivityRecord getUndoRecord( )
	{
		return undoStack.isEmpty( ) ? null : (ActivityRecord) undoStack.peek( );
	}
	/**
	 * Returns the label of the record at the top of the undo stack. The label
	 * describes the next operation to be undone.
	 * 
	 * @return The undo label, or null if there is no record to be undone.
	 */
	public String getUndoLabel( )
	{
		IActivityRecord cmd = getUndoRecord( );
		if ( cmd == null )
			return null;
		
		
		String label = cmd.getLabel( );
		assert label != null;
		return label;
	}