Bug 192789 Support to render reportlet using bookmark in frameset servlet.
Description: Support to render reportlet using bookmark in frameset servlet. At present, only run and preview servlet support __isreportlet&__bookmark to generate reportlet.
viewer/org.eclipse.birt.report.viewer/birt/WEB-INF/classes/org/eclipse/birt/report/service/ReportEngineService.java
/**
	 * Report engine instance.
	 */
	private IReportEngine engine = null;
	/**
	 * Static engine config instance.
	 */
	private EngineConfig config = null;
	/**
	 * URL accesses images.
	 */
	private String imageBaseUrl = null;
	/**
	 * Image handler instance.
	 */
	private HTMLServerImageHandler imageHandler = null;
	/**
	 * Web app context path.
	 */
	private String contextPath = null;
	/**
	 * Constructor.
	 * 
	 * @param servletContext
	 * @param config
	 */
	private ReportEngineService( ServletContext servletContext )
	{
		System.setProperty( "RUN_UNDER_ECLIPSE", "false" ); 
		if ( servletContext == null )