Bugs in plot3d and mgnuplot



Hi,
I run across a bug with parametric plots:

  Maxima version: 5.9.0.1cvs
  Maxima build date: 16:24 5/9/2004
  host type: i686-pc-linux-gnu
  lisp-implementation-type: CLISP
  lisp-implementation-version: 2.28 (released 2002-03-03) (built 3233846338) (memory 3293105089)

  (C5) plot3d([cos(x)*(3+y*cos(x/2)),sin(x)*(3+y*cos(x/2)),y*sin(x/2)],[x,-%pi,%pi],[y,-1,1]);
  Maxima encountered a Lisp error:

   symbol FIXNUM has no value

I also get an error when trying to use mgnuplot, because it has not been
made "executable" by make:

  (C6) plot3d(2^(-u^2+v^2),[u,-5,5],[v,-7,7],[plot_format,mgnuplot]);
  /bin/bash: line 1: /home/villate/cvs.sourceforge.net/maxima/plotting/mgnuplot: Permission denied

I can solve that easily with a "chmod +x mgnuplot", but shouldn't make do it?
it does in the case of omplotdata.

Regards,
Jaime