Bug 188283 Bubbles should be z-sorted by size in Bubble charts
Biggest bubbles should be drawn first so that there is no small bubble hidden by a bigger one.
chart/org.eclipse.birt.chart.engine/src/org/eclipse/birt/chart/event/MarkerInstruction.java
{
	private final DeferredCache dc;
	private final int iInstruction;
	private final double iMarkerSize;
	private final PrimitiveRenderEvent pre;
	public MarkerInstruction( DeferredCache dc, PrimitiveRenderEvent pre,
			int iInstruction, double iMarkerSize )
	{
		this.dc = dc;
		this.pre = pre;
		this.iInstruction = iInstruction;
		this.iMarkerSize = iMarkerSize;
	}
	public int compareTo( Object o )
	{
		if ( o instanceof MarkerInstruction )
		{
			
			return (int) ( ( (MarkerInstruction) o ).getMarkerSize( ) - iMarkerSize );
		}
		Bounds bo = null;
		if ( o instanceof PrimitiveRenderEvent )
		{
			try
			{
				bo = ( (PrimitiveRenderEvent) o ).getBounds( );
			}
			catch ( ChartException e )
			{