bug#61069: 30.0.50; comint-copy-old-input should include continuation lines

[Eli Zaretskii]

> From: Robert Pluim <rpluim@gmail.com>
> Cc: Eli Zaretskii <eliz@gnu.org>,  61069@debbugs.gnu.org
> Date: Fri, 31 Mar 2023 10:07:08 +0200
> 
> >>>>> On Thu, 30 Mar 2023 12:51:53 -0700, Bob Rogers <rogers@rgrjr.com> said:
> 
>     Bob> Ping?
> 
>     Bob>                                      -- Bob
> 
> Sorry, I didnʼt realize you were waiting on us. Eli, I can commit this
> to master later today.

Thanks, please do.  However, this:

> +(defcustom shell-get-old-input-include-continuation-lines nil
> +  "Whether `shell-get-old-input-default' includes \"\\\" lines."

seems to refer to a symbol that doesn't exist?