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
/**
	 * @param itemType the type of the extended item, i.e., "chart"
	 * @return an object that is used for query preparation time extended item processing 
	 */
	public IReportItemQuery createQueryItem(String itemType)
	{
		IConfigurationElement config = (IConfigurationElement)queryExtensions.get(itemType);
		if (config != null)
		{
			Object object = createObject(config, "class"); 
			if (object instanceof IReportItemQuery)
			{
				return (IReportItemQuery)object;
			}
		}
		return null;
	}
	
	/**
	 * @param format the format that the extension point supports
	 * @return an emitter
	 */
	public IContentEmitter createEmitter(String format, String id)
	{
		if(format==null)
		{
			return null;
		}
		IConfigurationElement config = null;
		for(int i=0; i<emitterExtensions.size(); i++)