Function: plotpoints
Class: highlevel
Section: graphic
C-Name: rectpoints
Prototype: vLGG
Help: plotpoints(w,listx,listy): draws in rectwindow w the points whose x
 (resp y) coordinates are in listx (resp listy). If listx and listy are both
 single values (i.e not vectors), draw the corresponding point (and move
 cursor)

