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
* convert the Y coordinate of a point from layout to Y coordinate in PDF
	 * @param layoutY 		the Y coordinate specified from layout
	 * @return				the PDF Y coordinate
	 */
	private float layoutPointY2PDF (int layoutY)
	{
		return pageHeight - pdfMeasure(layoutY);
	}
	
	/**
	 * convert the left X coordinate of an Area from layout 
	 * to the left X coordinate in PDF
	 * @param layoutX 		the X coordinate specified from layout
	 * @return				the PDF X coordinate
	 */
	private float layoutAreaX2PDF(int layoutX)
	{
		return pdfMeasure(layoutX);
	}
	
	/**
	 * convert the top Y coordinate of an Area from layout 
	 * to the bottom Y coordinate in PDF
	 * @param layoutY 		the Y coordinate specified from layout
	 * @param areaHeight	the height of the area whose coordinate need to be converted.
	 * 						To text area, the height is from the top of the text to
	 * 						the text's baseline.
	 * @return				the PDF Y coordinate
	 */
	private float layoutAreaY2PDF (int layoutY, int areaHeight)