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/impl/aggregation/sort/AggregationSortHelper.java
* @param filteredAggrResultSet
	 * @return
	 * @throws IOException
	 */
	private static List createMatchedAggrRow( IAggregationResultSet base,
			SortKey[] sortKeys ) throws IOException
	{
		List keyValues = new ArrayList();
		for ( int x = 0; x < sortKeys.length; x++ )
		{
			SortKey key = sortKeys[x];
			Object[] values = new Object[key.getLevelKeyIndex( )
					+ 1 - key.getLevelKeyOffset( )];
			boolean[] direction = new boolean[key.getLevelKeyIndex( )
					+ 1 - key.getLevelKeyOffset( )];
			
			
			for ( int y = key.getLevelKeyOffset( ); y < key.getLevelKeyIndex( ) + 1; y++ )
			{
				DimLevel level = sortKeys[x].getTargetResultSet( )
						.getLevel( y );
				values[y - key.getLevelKeyOffset( )] = base.getLevelKeyValue( base.getLevelIndex( level ) )[0];
				direction[y - key.getLevelKeyOffset( )] = base.getSortType( base.getLevelIndex( level ) ) == 1
						? false : true;
			}
			for ( int i = 0; i < key.getAggrKeys( ).length; i++ )
			{
				IAggregationResultRow row = getNextMatchRow( key.getFilteredResultSet( )[i],
						values,
						direction,