bug#28597: 26.0.60; [Security] Configure should use --without-pop by default

[Eli Zaretskii <eliz@gnu.org>]

> From: nljlistbox2@gmail.com (N. Jackson)
> Cc: Eli Zaretskii <eliz@gnu.org>,  jwiegley@gmail.com,  28597@debbugs.gnu.org,  rpluim@gmail.com
> Date: Tue, 03 Oct 2017 10:29:16 -0400
> 
> I was thinking of disabling the commands in question in the case
> that they will be insecure and prompting along the lines of:
> 
>   You have typed abc, invoking disabled command xyz.
> 
>   Beware: This command retrieves POP3 email via only insecure
>   channels. See [reference to relevant documentation] for more
>   information.
> 
>   Do you want to use this command anyway?
> 
>   You can now type
>   y   to try it and enable it (no questions if you use it again).
>   n   to cancel--don't try the command, and it remains disabled.
>   SPC to try the command just this once, but leave it disabled.
>   !   to try it, and enable all disabled commands for this session only.
> 
> This informs the user but only does so once (if they don't want to
> be told again); after that they need not see the warning ever
> again. Telling someone something once really cannot be described
> as "nagging".

I don't see how can we do such a thing, since movemail is a
command-line utility written in C, not a Lisp program.  People can
(and some do) invoke movemail from the shell prompt.