Bug 177504 Engine doesn't provide SubQuery for extended item
Engine doesn't provide SubQuery for extended item, so chart can't use container's binding to execute the query. If possible, engine could provide an option for extended item to choose whether engine could create the query, so extended item won't create SubQuery by itself.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/data/dte/ReportQueryBuilder.java
*      queries array of this design
	 */
	public IDataQueryDefinition[] build( IDataQueryDefinition parentQuery, ReportItemDesign design )
	{
		synchronized ( report )
		{
			
			
			Object result = design.accept( queryBuilder, parentQuery );
			
			if ( result == null )
			{
				return null;
			}
			IDataQueryDefinition[] queries = (IDataQueryDefinition[]) result;
				
			design.setQueries( queries );
			for ( int i = 0; i < queries.length; i++ )
			{
				IDataQueryDefinition query = queries[i];
				if ( query != null )
				{						
					this.queryIDs.put( query, String.valueOf( design
							.getID( ) )
							+ "_" + String.valueOf( i ) );
					
					if ( query instanceof IBaseQueryDefinition )
					{
						ResultMetaData metaData = new ResultMetaData( (IBaseQueryDefinition)query );
						resultMetaData.put( query, metaData );