bug#58843: Print "decrypted" rot13 text is buffer is read-only

[Eli Zaretskii <eliz@gnu.org>]

> From: Philip Kaludercic <philipk@posteo.net>
> Cc: 58843@debbugs.gnu.org
> Date: Sat, 29 Oct 2022 06:28:43 +0000
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> > Showing the result in the echo-area is a good idea, but echo-area is
> > not really suitable for displaying arbitrarily long text.  How about
> > popping a window with a temporary buffer instead?
> 
> Is there a way to re-use shell-command's behaviour of displaying short
> messages in the echo area and longer messages in a separate buffer?

It's a few lines in shell-command, so you could reuse them, or make a
utility function out of them.

> Popping up a buffer just for one or two lines can be annoying,
> especially if the information is not something you want to keep around.

Sure, that would be even better.  Although in that case we'd need to
change what the manual says about the command, because it explicitly
says we show the encoded text in another window.