Bug 128586 Change parameter in drill through link doesn't work in pdf.
Description: Change parameter in drill through link doesn't work in pdf. Steps to reproduce: 1. New a report source and a report target. 2. Insert a report parameter p1 in target.rptdesign, drag it to Layout. 3. Insert a label in source.rptdesign, define a drill through link to target.rptdesign and set p1 to "first". 4. Preview source.rptdesign in pdf and click the link. 5. Revise drill through link to set p1 to "second", then preview in pdf, click the link. Expected result: Target show "second" as value. Actual result: Target still showed "first"
engine/org.eclipse.birt.report.engine.emitter.pdf/src/org/eclipse/birt/report/engine/emitter/pdf/PDFEmitter.java
* @param imageURI		the URI referring the image
	 * @param x				the start X coordinate at the pdf where the image is positioned
	 * @param y				the start Y coordinate at the pdf where the image is positioned
	 * @param width			the width of the background dimension
	 * @param height		the height of the background dimension
	 * @param positionX		the offset X percentage relating to start X
	 * @param positionY		the offset Y percentage relating to start Y
	 * @param repeat		the background-repeat property
	 */
	private void drawBackgroundImage(String imageURI, float x, float y, 
			float width, float height, float positionX, float positionY, String repeat)
	{
		
		if ( null == imageURI )
		{
			return;
		}
		
		String id = imageURI;
		if (reportDesign != null)
		{
			URL url = reportDesign.findResource(imageURI, IResourceLocator.IMAGE);
			if (url != null)
			{
				id = url.toExternalForm();
			}
		}
		
		if(id==null || "".equals(id)) 
		{