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/executor/ExtendedItemExecutor.java
* <li> process the stylies, visiblity, bookmark and actions.
	 * <li> create the generator to process the object
	 * <li> call the onCreate if needed.
	 * <li> save the generate states into the foreign object
	 * <li>
	 * 
	 * @see org.eclipse.birt.report.engine.executor.ReportItemExcutor#execute(IContentEmitter)
	 */
	
	public IContent execute( )
	{
		
		ExtendedItemHandle handle = (ExtendedItemHandle) design.getHandle( );
		String tagName = handle.getExtensionName( );
		executor = ExtensionManager.getInstance( ).createReportItemExecutor(
				tagName );
		if ( executor != null )
		{
			
			executor.setContext( executorContext );
			executor.setModelObject( handle );
			if (parent instanceof ExtendedItemExecutor)
			{
				executor.setParent( ((ExtendedItemExecutor)parent).executor );
			}
			else
			{
				executor.setParent( parent );
			}