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
* </nl>
	 * 
	 * @return <code>true</code> if {@link #redo()}can be called.
	 */
	public boolean canRedo( )
	{
		if ( !transStack.isEmpty( ) )
			return false;
		else if ( redoStack.size( ) == 0 )
			return false;
		else
		{
			ActivityRecord record = (ActivityRecord) redoStack.lastElement( );
			return record.canUndo( );
		}
	}
	/**
	 * If the undo stack has grown too large, discard the oldest entries.
	 */
	private void trimUndoStack( )
	{
		while ( undoStack.size( ) > stackLimit )
		{
			ActivityRecord cmd = (ActivityRecord) undoStack.remove( 0 );
			assert cmd.getState( ) != ActivityRecord.DISCARD_STATE;
			cmd.destroy( );
			cmd.setState( ActivityRecord.DISCARD_STATE );
		}
	}
	/**