implicit_plot broken in 5.20.1?



(%i3) load(implicit_plot);
(%o3) 
C:/PROGRA~1/MAXIMA~2.1/share/maxima/5.20.1/share/contrib/implicit_plot.lisp

>From the user documentation:

(%i9) implicit_plot (x^2 = y^3 - 3*y + 1, [x, -4, 4], [y, -4, 4], 
[gnuplot_preamble, "set zeroaxis"]);
Maxima encountered a Lisp error:
 Error in GNUPLOT-PRINT-HEADER [or a callee]: GNUPLOT-PRINT-HEADER [or a 
callee] requires more than one argument.

Maybe this has been reported or fixed...I was going do some implicit plots 
in class this morning :(
Workaround?

--Barton