Show/Hide changes in menu-bar.el

["Eli Zaretskii" <eliz@is.elta.co.il>]

Recent changes in menu-bar.el used window-system to decide whether to
show certain display options in the menu.  Please avoid using
window-system as much as possible (not only fo the menu bar).  It is
the wrong tool to make such decisions.  In this particular case, it
actually did the wrong thing, since the MS-DOS port defines a non-nil
value for window-system, but doesn't support a tool bar and the scroll
bars.

It is best to condition on some symbol or function being bound: this
way, if/when the relevant feature gets implemented on the platforms
where it is currently unavailable, the menu bar will automatically
DTRT.  If you cannot find a symbol or a function, please use
display-*-p functions, as suggested by the ELisp manual.

Thanks.