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
}
	private static void populateEmptySortKey( IAggregationResultSet base,
			SortKey[] sks )
	{
		for ( int i = 0; i < sks.length; i++ )
		{
			if ( sks[i] == null )
			{
				sks[i] = new SortKey( new int[0], new boolean[0], i, 0, base, new AxisQualifier[0] );
			}
		}
	}
	private static IDiskArray getDiskArrayFromAggregationResultSet(
			IAggregationResultSet base ) throws IOException
	{
		IDiskArray diskArray = new BufferedStructureArray( AggregationResultRow.getCreator( ),
				4096 );
		for ( int j = 0; j < base.length( ); j++ )
		{
			base.seek( j );
			IAggregationResultRow temp = base.getCurrentRow( );
			diskArray.add( temp );
		}
		if( base.length( ) > 0 )
		{
			base.seek( 0 );
		}
		return diskArray;
	}
	private static void createFilteredResultSet(