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/query/view/QueryExecutor.java
assert executor.getCubeQueryDefinition( ).getQueryResultsID( ) != null;
			
			rs = AggregationResultSetSaveUtil.load( executor.getCubeQueryDefinition( )
					.getQueryResultsID( ),
					executor.getContext( ).getDocReader( ),new VersionManager( executor.getContext()).getVersion( ));
		}
		else
		{
			
			rs = cubeQueryExcutorHelper.execute( aggrDefns, stopSign );
		}
		cube.close( );
		return new CubeResultSet( rs, view, manager, cubeQueryExcutorHelper );
	}
	/**
	 * Populate the Result Set, either by re-execution ( If it has not been executed yet ) or 
	 * get it from local time folder.
	 * @param executor
	 * @param aggrDefns
	 * @param cubeQueryExcutorHelper
	 * @return
	 * @throws IOException
	 * @throws BirtException
	 */
	private IAggregationResultSet[] populateRs( CubeQueryExecutor executor,
			AggregationDefinition[] aggrDefns,
			CubeQueryExecutorHelper cubeQueryExcutorHelper, boolean saveToRD )
			throws IOException, BirtException
	{
		IAggregationResultSet[] rs;