Utility function. Used for transforming rectangular facets coded
in three matrices x,y,z to scilab code for facets accepted by plot3d.
Examples
//A sphere...u=linspace(-%pi/2,%pi/2,40);v=linspace(0,2*%pi,20);x=cos(u)'*cos(v);y=cos(u)'*sin(v);z=sin(u)'*ones(v);//plot3d2(x,y,z) is equivalent to...[xx,yy,zz]=nf3d(x,y,z);plot3d(xx,yy,zz)