bug#27122: 26.0.50; [PATCH] Add customizable to display unprintables as hex

[Eli Zaretskii]

> Date: Mon, 29 May 2017 22:15:58 +0200
> From: Vasilij Schneidermann <v.schneidermann@gmail.com>
> Cc: 27122@debbugs.gnu.org
> 
> > Does "C-x =" or "C-u C-x =" fit the bill in this case?  If the former
> > doesn't, how about adding the hex byte translation to what it shows?
> 
> This is the crutch I'm currently using.  It isn't practical for more
> than a few characters.  If I considered it sufficient, I wouldn't be
> handing in a patch.

Well, you didn't mention this at all, so I couldn't know.

OK, please submit the patch with the necessary documentation, and
please add a test for the original and the new behavior.

Also, I think the option should be called display-raw-bytes-as-hex,
since "unprintables", though more accurate, is IMO too technical for
most users, and the default behavior limits this display to raw bytes.

Finally, I think it would be good to make this option a defcustom, so
please add the necessary glue to cus-start.el.

Btw, is \xNN what people are used to in this kind of display?  Emacs
generally uses #xNN elsewhere, but if \xNN is more familiar, I don't
mind.

Thanks.

P.S.  A minor nit: we use tabs and spaces to indent C code, not just
spaces.