Usage: SET SCROLL_LINES [<number of screen lines to scroll>]
  This allows you to set the number of lines the screen will
  scroll each time the cursor reaches the bottom of the screen.
  If SCROLL_LINES is set to 0, the SCROLL is turned OFF as well,
  and must be turned back on before scrolling can be resumed.
  The maximum number of lines that may be scrolled is the size of
  the display (the number of lines on the screen minus 2).
  Negative numbers are automatically changed to positive.
