Function: plotlines
Section: graphic
C-Name: plotlines
Prototype: vLGGD0,L,
Help: plotlines(w,X,Y,{flag=0}): draws an open polygon in rectwindow
 w where X and Y contain the x (resp. y) coordinates of the vertices.
 If X and Y are both single values (i.e not vectors), draw the
 corresponding line (and move cursor). If (optional) flag is nonzero, close
 the polygon.
Doc: draw on the rectwindow $w$
 the polygon such that the (x,y)-coordinates of the vertices are in the
 vectors of equal length $X$ and $Y$. For simplicity, the whole
 polygon is drawn, not only the part of the polygon which is inside the
 rectwindow. If $\fl$ is nonzero, close the polygon. In any case, the
 virtual cursor does not move.

 $X$ and $Y$ are allowed to be scalars (in this case, both have to).
 There, a single segment will be drawn, between the virtual cursor current
 position and the point $(X,Y)$. And only the part thereof which
 actually lies within the boundary of $w$. Then \emph{move} the virtual cursor
 to $(X,Y)$, even if it is outside the window. If you want to draw a
 line from $(x1,y1)$ to $(x2,y2)$ where $(x1,y1)$ is not necessarily the
 position of the virtual cursor, use \kbd{plotmove(w,x1,y1)} before using this
 function.
