bug#28797: 26.0.90; Improve printing of error on catching file-error in dired

[Eli Zaretskii]

> From: Noam Postavsky <npostavs@users.sourceforge.net>
> Cc: 28797@debbugs.gnu.org,  tino.calancha@gmail.com,  kaushal.modi@gmail.com
> Date: Fri, 13 Oct 2017 09:15:01 -0400
> 
> Eli Zaretskii <eliz@gnu.org> writes:
> 
> >> Here's a patch, uses error-message-string for #1,
> >
> > This doesn't handle all of the parts of the complaint, does it?
> 
> The resulting error will look like
> 
>     file-error: Non-regular file: Is a directory, /home/kmodi/.emacs.d/foo
> 
> It's not quite the perfect sentence envisioned on the OP, but it gets
> all the information across, with punctuation separating the parts.

OK, close enough for me.

> >> condition-case-unless-debug for #2.
> >
> > This is quite a radical change in very old behavior, so if it is
> > deemed a good idea, it should go to master.
> 
> Hmm, it doesn't seem that radical to me, but I don't have a problem
> putting it only to master, or even not doing that at all and just saying
> the user should use debug-on-signal.

It's radical because we never produce backtrace in similar cases
anywhere else in Emacs.

Let's wait to hear what others think about this part.

Thanks.