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
contentByte.moveTo(startX, startY);
		contentByte.setLineWidth(width);
		contentByte.lineTo(endX, endY);        
		contentByte.setColorStroke(color);
		contentByte.stroke();
	}
	
	/**
	 * draw the background color at the contentByteUnder of the pdf
	 * @param color			the color to be drawed
	 * @param x				the start X coordinate
	 * @param y				the start Y coordinate
	 * @param width			the width of the background dimension
	 * @param height 		the height of the background dimension
	 */
	private void drawBackgroundColor(Color color, float x, float y, float width, float height)
	{
		if (null == color)
		{
			return;
		}
		cbUnder.saveState();
		cbUnder.setColorFill(color);
		cbUnder.rectangle(x, y-height, width, height);
		cbUnder.fill();
		cbUnder.restoreState();
	}
	
	/**
	 * draw the backgound image at the contentByteUnder of the pdf with the given offset