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
/**
	 * create the static instance. It is a separate function so that getInstance do not need to be synchronized
	 */
	private synchronized static void createInstance()
	{
		if (sm_instance == null)
			sm_instance = new ExtensionManager();
	}
	
	/**
	 * @return the single instance for the extension manager 
	 */
	static public ExtensionManager getInstance()
	{
		if (sm_instance == null)
			createInstance();
		
		return sm_instance;
	}
	/**
	 * @param itemType 
	 * @return an object that is used for generation time extended item processing 
	 */
	public IReportItemExecutor createReportItemExecutor(String itemType)
	{
		IConfigurationElement config = (IConfigurationElement) generationExtensions
				.get( itemType );
		if ( config != null )
		{
			Object object = createObject( config, "class" );