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/RunAndRenderTask.java
{
	/**
	 * specifies the emitter ID used for rendering the report
	 */
	protected String emitterID;
	
	protected IReportLayoutEngine layoutEngine;
	/**
	 * @param engine
	 *            reference to the report engine
	 * @param runnable
	 *            the runnable report design reference
	 */
	public RunAndRenderTask( IReportEngine engine, IReportRunnable runnable )
	{
		super( engine, runnable );
	}
	protected IContentEmitter createContentEmitter( ) throws EngineException
	{
		String format = executionContext.getOutputFormat( );
		ExtensionManager extManager = ExtensionManager.getInstance( );
		boolean supported = false;
		Collection supportedFormats = extManager.getSupportedFormat( );
		Iterator iter = supportedFormats.iterator( );
		while ( iter.hasNext( ) )