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
* stores all the mime types that are supported
	 */
	protected HashMap formats = new HashMap();
	
	protected HashMap emitters = new HashMap();
	/**
	 * HTML pagination.
	 */
	public static final String PAGE_BREAK_PAGINATION = "page-break-pagination";
	/**
	 * Pdf pagination.
	 */
	public static final String PAPER_SIZE_PAGINATION = "paper-size-pagination";
	/**
	 * No pagination.
	 */
	public static final String NO_PAGINATION = "no-pagination";
	
	
	/**
	 * Dummy constructor
	 */
	ExtensionManager()
	{
		loadGenerationExtensionDefns();
		loadPresentationExtensionDefns();
		loadQueryExtensionDefns();
		loadEmitterExtensionDefns();
	}