bug#24413: 24.5; doc string of `whitespace-mode' does not mention Lisp `toggle' arg

[Drew Adams]

In this respect, the explicit doc string provided when defining
`whitespace-mode' is _worse_ than the default doc string provided by
`define-minor-mode'.  The latter at least adds this important
information, which is missing from `C-h f whitespace-mode':

  "and toggle it if ARG is `toggle'."

This might not be the only minor mode whose doc fails to mention
`toggle' as ARG for Lisp.

See http://emacs.stackexchange.com/a/27006/105.

In GNU Emacs 24.5.1 (i686-pc-mingw32)
 of 2015-04-11 on LEG570
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --prefix=/c/usr --host=i686-pc-mingw32'