Bug 182895 Support sort on Level attribute.
Currently in OLAP engine we only support sort on level key value. We should go ahead to support sort on level attribute value.
data/org.eclipse.birt.data/src/org/eclipse/birt/data/engine/olap/data/api/CubeQueryExecutorHelper.java
* @throws DataException
	 */
	private int findMatchedResultSetIndex( IAggregationResultSet[] rSets, IAggregationResultSet source ) throws DataException
	{
		for( int i = 0; i < rSets.length; i++ )
		{
			if( AggrSortHelper.isEdgeResultSet( rSets[i] ))
			{
				if( source.getLevel( 0 ).equals( rSets[i].getLevel( 0 ) ))
					return i;
			}
		}
		throw new DataException("Invalid");
	}
	
	/**
	 * This method is responsible for computing the aggregation result according
	 * to the specified aggregation definitions.
	 * @param aggregations
	 * @param stopSign
	 * @return
	 * @throws DataException
	 * @throws IOException
	 * @throws BirtException
	 */
	private IAggregationResultSet[] onePassExecute(
			AggregationDefinition[] aggregations, StopSign stopSign )
			throws DataException, IOException, BirtException
	{
		IDiskArray[] dimPosition = getFilterResult( );