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/AggrSortHelper.java
{
				if ( isEdgeResultSet( resultSet[i] )
						&& ( resultSet[i].getLevelIndex( (DimLevel)keys[0] ) >= 0 ) )
				{
					base = resultSet[i];
					break;
				}
			}
			return AggregationSortHelper.sort( base, sortKeys );
		}
		catch ( IOException e )
		{
			throw new DataException( e.getLocalizedMessage( ) );
		}
	}
	/**
	 * A result set would come to be an edge result set only if its aggregation function is null.
	 * @param resultSet
	 * @return
	 */
	public static boolean isEdgeResultSet( IAggregationResultSet resultSet )
	{
		return ( resultSet.getAggregationDefinition( ) == null || resultSet.getAggregationDefinition( )
				.getAggregationFunctions( ) == null );
	}
	/**
	 * 
	 * @param resultSet
	 * @param levelNames
	 * @return