Function: plotlines
Class: highlevel
Section: graphic
C-Name: rectlines
Prototype: vLGGD0,L,
Help: plotlines(w,listx,listy,{flag=0}): draws an open polygon in rectwindow
 w where listx and listy contain the x (resp. y) coordinates of the vertices.
 If listx and listy are both single values (i.e not vectors), draw the
 corresponding line (and move cursor). If (optional) flag is non-zero, close
 the polygon

