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/render/DeferredCache.java
{
			if ( pre instanceof I3DRenderEvent )
			{
				al3D.add( new WrappedInstruction( this,
						pre.copy( ),
						iInstruction ) );
			}
			else
			{
				alPlanes.add( new WrappedInstruction( this,
						pre.copy( ),
						iInstruction ) );
			}
		}
		catch ( ChartException ufex )
		{
			logger.log( ufex );
		}
	}
	
	/**
	 * Adds rendering Plane event to cache. This Plane is usually a shadow or
	 * depth, and will be in the lower z-order
	 * 
	 * @param pre
	 *            As of now, supported types are RectanguleRenderEvent and
	 *            PolygonRenderEvent
	 */
	public final void addPlaneShadow( PrimitiveRenderEvent pre, int iInstruction )
	{