bug#22813: 24.5; doc string of `apropos-variable' - mention C-u

[Eli Zaretskii]

> From: Kaushal Modi <kaushal.modi@gmail.com>
> Date: Fri, 26 Feb 2016 08:15:27 -0500
> 
> --- a/lisp/apropos.el
> +++ b/lisp/apropos.el
> @@ -505,7 +505,7 @@ apropos-user-option
>  ;;;###autoload
>  (defun apropos-variable (pattern &optional do-not-all)
>    "Show variables that match PATTERN.
> -When DO-NOT-ALL is non-nil, show user options only, i.e. behave
> +With prefix argument DO-NOT-ALL non-nil, show user options only, i.e. behave
>  like `apropos-user-option'."

Thanks.

However, this is not the best way of expressing the behavior wrt
prefix arguments.  Here's an example of how we do this elsewhere:

  (defun jump-to-register (register &optional delete)
    "Move point to location stored in a register.
  If the register contains a file name, find that file.
  \(To put a file name in a register, you must use `set-register'.)
  If the register contains a window configuration (one frame) or a frameset
  \(all frames), restore that frame or all frames accordingly.
  First argument is a character, naming the register.
  Optional second arg non-nil (interactively, prefix argument) says to
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  delete any existing frames that the frameset doesn't mention.
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^