Bug 159076 PDF emitter needs to response if "com.lowagie.itext" is missed.
Previously on GUI, preview in PDF has to check the "com.lowagie.itext" is included in BIRT firstly. Now we think GUI doesn't need to do any check for emitters and in order to avoid any hard coded behaviors about emitter contribution, this check is remove from GUI codes. So, PDF emitter should be responsible to response if required resources is missed.
engine/org.eclipse.birt.report.engine/src/org/eclipse/birt/report/engine/api/impl/RenderTask.java
/* (non-Javadoc)
	 * @see org.eclipse.birt.report.engine.api.IRenderTask#setInstanceID( InstanceID iid )
	 */
	public void setInstanceID( InstanceID iid ) throws EngineException
	{
		innerRender = new ReportletRender( iid );
	}
	/* (non-Javadoc)
	 * @see org.eclipse.birt.report.engine.api.IRenderTask#setPageRange( String pageRange )
	 */
	public void setPageRange( String pageRange ) throws EngineException
	{
		innerRender = new PageRangeRender( parsePageSequence( pageRange, reportDoc.getPageCount( )) );
	}
	/* (non-Javadoc)
	 * @see org.eclipse.birt.report.engine.api.IRenderTask#setBookmark( String bookmark )
	 */
	public void setBookmark( String bookmark ) throws EngineException
	{
		long pageNumber = reportDoc.getPageNumber( bookmark );
		if ( pageNumber <= 0 ) {
			throw new EngineException( "Can not find bookmark :{0}", bookmark ); 
		}
		innerRender = new PageRender( pageNumber );
	}
	public void setReportlet( String bookmark ) throws EngineException
	{
		innerRender = new ReportletRender( bookmark ); 
	}
	private abstract class InnerRender