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
/**
	 * Determines if the record stack has a record to undo. There is a record to
	 * undo if
	 * <nl>
	 * <li>no transaction is active,</li>
	 * <li>the undo stack is not empty, and
	 * <li>the top record can be undone.</li>
	 * </nl>
	 * 
	 * @return <code>true</code> if {@link #undo()}can be called
	 */
	public boolean canUndo( )
	{
		if ( !transStack.isEmpty( ) )
			return false;
		else if ( undoStack.size( ) == 0 )
			return false;
		else
		{
			ActivityRecord record = (ActivityRecord) undoStack.lastElement( );
			return record.canUndo( );
		}
	}
	/**
	 * Determines if the record stack has a record to redo. There is a record to
	 * redo if
	 * <nl>
	 * <li>no transaction is active,</li>
	 * <li>the redo stack is not empty, and</li>
	 * <li>the top record can be redone.</li>