VEraseOverlayRectangle - erases a 1-bit overlay rectangle.
  VEraseOverlayRectangle(win, ovl, xloc, yloc, width, height)
  Window win;
  int ovl;
  int xloc, yloc;
  int width, height;
  VEraseOverlayRectangle erases a 1-bit overlay rectangle in the image
Return Value
  0 - work successfully.
  6 - invalid window ID.
  225 - no overlay created.
  237 - the overlay is not on.
  win - the image window ID or one of its subwindows' ID.
  ovl - specifies the overlay number to be used to erase the rectangle.
  xloc, yloc - specifies x and y coordinates of the upper left corner of the
        rectangle, relative to the origin of the specified window.
  width, height - specifies the width and height in pixels of the frame.
Side Effects
  Any other graphics in that overlay on that rectangle will also be erased.
Entry Conditions
  If ovl, xloc, yloc, width, or height is not valid, or VCreateColormap is
not called earlier, or the rectangle to be drawn is totally out of the
specified window boundary, VEraseOverlayRectangle prints an error message
to the standard error stream, produces a core dump file and exits from the
current process.
Related Functions
VDisplayOverlayRectangle, VEraseOverlay, VTurnOffOverlay.