Function: plotell
Section: graphic
C-Name: plotell
Prototype: vLGGD0,L,
Help: plotell(w,x2,y2,{filled=0}): if the cursor is at position (x1,y1), draw the
 ellipse that fits inside the box with diagonal (x1,y1) and (x2,y2) in rectwindow w
 (cursor does not move).
 If filled=1, fill the ellipse
Doc: let $(x1,y1)$ be the current position of the virtual cursor. Draw in the
 rectwindow $w$ the outline of the ellipse that fits inside the box such that the points
 $(x1,y1)$ and $(x2,y2)$ are opposite corners. The virtual cursor does \emph{not} move.
 If $\var{filled}=1$, fill the ellipse.
