Since drawMultiplePies is only implemented in PiePlot, but
not in Pie3DPlot, even though you can create a Pie3DPlot
with multiple series (using a CategoryDataPlot and setting
the extractType), it will always currently draw them in 2D
since the PiePlot draw routine is called (took a while to
figure this one out).
Shouldn't be hard, since the logic is already there in