(auto_resize_tool_bars_p): Replace with ...

(auto_resize_tool_bars_p): Replace with ...
(Vauto_resize_tool_bars): ... this.
(syms_of_xdisp): DEFVAR_LISP and initialize it.  Update doc string
to describe new value `grow-only', and use of C-l.
(display_tool_bar_line): Only use default face for border below
toolbar if not grow-only (to get acceptable visual appearence).
Explicitly set visible_height for empty toolbar lines.
(redisplay_tool_bar): Handle `grow-only' setting.  Check and clear
minimize_tool_bar_window_p flag.