bug#28936: enhancement request: remove vertical scroll bar automatically when not needed

[Keith David Bershatsky]

Here is a first draft with a simple test (modifying xdisp.c), which probably 
nukes more than just the selected window's scroll bars when removing them, but 
it may be sufficient to revive this enhancement request in the event anyone is 
interested.

 finish_scroll_bars:

   if ((WINDOW_HAS_VERTICAL_SCROLL_BAR (w) || WINDOW_HAS_HORIZONTAL_SCROLL_BAR 
(w))
        && ZV - BEGV > BUF_Z (XBUFFER (w->contents)) - w->window_end_pos - 
marker_position (w->start))
    {
      if (WINDOW_HAS_VERTICAL_SCROLL_BAR (w))
        /* Set the thumb's position and size.  */
        set_vertical_scroll_bar (w);

      if (WINDOW_HAS_HORIZONTAL_SCROLL_BAR (w))
        /* Set the thumb's position and size.  */
        set_horizontal_scroll_bar (w);

      /* Note that we actually used the scroll bar attached to this
         window, so it shouldn't be deleted at the end of redisplay.  */
      if (FRAME_TERMINAL (f)->redeem_scroll_bar_hook)
        (*FRAME_TERMINAL (f)->redeem_scroll_bar_hook) (w);
    }
    else
      {
        (*FRAME_TERMINAL (f)->condemn_scroll_bars_hook) (f);
        (*FRAME_TERMINAL (f)->judge_scroll_bars_hook) (f);
      }


Keith