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/extension/internal/ExtensionManager.java
* load report item query extension definitions 
	 */
	protected void loadQueryExtensionDefns()
	{
		IExtensionRegistry registry = Platform.getExtensionRegistry(); 
		IExtensionPoint extPoint = registry.getExtensionPoint(EXTENSION_POINT_QUERY);
		if(extPoint==null)
			return;
		IExtension[] exts = extPoint.getExtensions();
		logger.log(Level.FINE, "Start load extension point: {0}", EXTENSION_POINT_QUERY); 
		for (int i = 0; i < exts.length; i++)
		{
			IConfigurationElement[] configs = exts[i].getConfigurationElements();
			for (int j = 0; j < configs.length; j++)
			{
				String itemName = configs[j].getAttribute("name"); 
				queryExtensions.put(itemName, configs[j]);
				logger.log(Level.FINE, "Load query extension: {0}", itemName); 
			}
		}
	}
	
	/**
	 * load report item emitters extension definitions
	 */
	protected void loadEmitterExtensionDefns()
	{
		IExtensionRegistry registry = Platform.getExtensionRegistry(); 
		IExtensionPoint extPoint = registry.getExtensionPoint(EXTENSION_POINT_EMITTERS);
		if(extPoint==null)