bug#12405: 24.2.50; doc of `menu-bar-mode' is incorrect

[Drew Adams]

The doc string says this:

"If called from Lisp, enable Menu Bar mode if ARG is omitted or nil."

That means that when called from Lisp (menu-bar-mode nil) and (menu-bar-mode)
should turn OFF the mode.  But they turn it ON instead.
 
The code for `menu-bar-mode' has this, which for ARG = nil sets
`menu-bar-mode' to t:
 
(setq menu-bar-mode
      (if (eq arg 'toggle)
   (not menu-bar-mode)
 (> (prefix-numeric-value arg) 0)))

(prefix-numeric-arg nil) = 1, which is > 0.
 
This bug is present also in release Emacs 24.1.  I haven't checked older
releases.
 
In GNU Emacs 24.2.50.1 (i386-mingw-nt5.1.2600)
 of 2012-09-02 on MARVIN
Bzr revision: 109861 eggert@cs.ucla.edu-20120902171035-7mzihil3xd6bjfiy
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.6) --no-opt --enable-checking --cflags
 -ID:/devel/emacs/libs/libXpm-3.5.8/include
 -ID:/devel/emacs/libs/libXpm-3.5.8/src
 -ID:/devel/emacs/libs/libpng-dev_1.4.3-1/include
 -ID:/devel/emacs/libs/zlib-dev_1.2.5-2/include
 -ID:/devel/emacs/libs/giflib-4.1.4-1/include
 -ID:/devel/emacs/libs/jpeg-6b-4/include
 -ID:/devel/emacs/libs/tiff-3.8.2-1/include
 -ID:/devel/emacs/libs/gnutls-3.0.9/include
 -ID:/devel/emacs/libs/libiconv-1.13.1-1-dev/include
 -ID:/devel/emacs/libs/libxml2-2.7.8/include/libxml2'