Bug#4356: menu-bar-mode flag argument is inconsistent with universe

[Ian Jackson <ian@chiark.chu.cam.ac.uk>]

Package: emacs
Version: 19.31-2

I used to have in my startup files
 (menu-bar-mode nil)
which used to turn off menu bars.

In 19.31 this has changed so that `nil' doesn't have the desired
effect.  Instead, you have to supply a negative number !

This is totally inconsistent with almost every other emacs-lisp
function.

menu-bar-mode should accept `nil' to turn menu bars off and `t' to
turn them on.  I don't have an opinion about whether positive and
negative numbers ought to be supported.

Ian.