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.tests/test/org/eclipse/birt/data/engine/olap/api/CubeFeaturesTest.java
/**
	 * top/bottom dimension filter.
	 * @throws Exception
	 */
	public void testAggrFilter2( ) throws Exception
	{
		ICubeQueryDefinition cqd = new CubeQueryDefinition( cubeName );
		IEdgeDefinition columnEdge = cqd.createEdge( ICubeQueryDefinition.COLUMN_EDGE );
		IEdgeDefinition rowEdge = cqd.createEdge( ICubeQueryDefinition.ROW_EDGE );
		IDimensionDefinition dim1 = columnEdge.createDimension( "dimension1" );
		IHierarchyDefinition hier1 = dim1.createHierarchy( "dimension1" );
		hier1.createLevel( "level11" );
		hier1.createLevel( "level12" );
		hier1.createLevel( "level13" );
		IDimensionDefinition dim2 = rowEdge.createDimension( "dimension2" );
		IHierarchyDefinition hier2 = dim2.createHierarchy( "dimension2" );
		hier2.createLevel( "level21" );
		createSortTestBindings( cqd );
		
		CubeFilterDefinition filter1 = new CubeFilterDefinition( new ConditionalExpression( "dimension[\"dimension2\"][\"level21\"]",
				IConditionalExpression.OP_BOTTOM_N,
				"3" ) );
		CubeFilterDefinition filter2 = new CubeFilterDefinition( new ConditionalExpression( "dimension[\"dimension1\"][\"level12\"]",
				IConditionalExpression.OP_TOP_N,
		"2" ) );
		cqd.addFilter( filter1 );
		cqd.addFilter( filter2 );
		DataEngine engine = DataEngine.newDataEngine( DataEngineContext.newInstance( DataEngineContext.DIRECT_PRESENTATION,
				null,
				null,