bug#44231: 27.1; Non-printable characters found. Continue sending?

[積丹尼 Dan Jacobson]

Today let's discuss this prompt:

      Non-printable characters found.  Continue sending?

      d: delete                r: replace               s: send                 
 e: edit
      Remove non-printable     Replace non-printable    Send as is without      
 Continue editing
      characters and send      characters with "."      removing anything
                               and send

1. The user has a right to pick a different character than ".".
And not just via .gnus.el, etc. So add a way to prompt for one.

2. In all cases the user has a right to continue editing after the
replacement, so please implement that.

E.g., the user wants to see how everything looks, and mention: 'Larry, as
you see above, I replaced the garbage characters with "X".'

3. Also offer to replace with \x12 \0x12 etc. formats.
as: the user might want to say "See Larry, I replaced that junk with
ASCII representations. So you can see all the different ones that you
sent me were."