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/WrappedInstruction.java
/*
	 * (non-Javadoc)
	 * 
	 * @see java.lang.Comparable#compareTo(java.lang.Object)
	 */
	public int compareTo( Object o )
	{
		Bounds bo = null;
		if ( o instanceof PrimitiveRenderEvent )
		{
			try
			{
				bo = ( (PrimitiveRenderEvent) o ).getBounds( );
			}
			catch ( ChartException e )
			{
				assert false;
				return -1;
			}
		}
		else if ( o instanceof WrappedInstruction )
		{
			bo = ( (WrappedInstruction) o ).getBounds( );
		}
		return (dc != null && dc.isTransposed( ) ) ? PrimitiveRenderEvent.compareTransposed( getBounds( ), bo )
				: PrimitiveRenderEvent.compareRegular( getBounds( ), bo );
	}
	/**
	 * Returns the associated event.
	 *