bug#18132: Time for a smarter dired-guess-shell-alist-default? (dired-x.el)

[Juri Linkov]

>> https://lists.gnu.org/archive/html/bug-gnu-emacs/2021-10/msg01952.html
>
> This says two things:
>
>   . some commands in the list are less capable then others
>   . XDG can do the job better
>
> To the first point, my response would be: put the better ones first in
> the list, but leave the worse ones in the list for those users who
> don't have the better alternatives.

I completely agree.  This is what I tried to do,
but couldn't find a way to refactor this amalgamation
in dired-guess-shell-alist-default.  We need to split it
to two parts, so users without XDG will have:

1. better ones from dired-guess-shell-alist-default
2. worse ones from dired-guess-shell-alist-default

And users with XDG should be able to have:

1. better ones from dired-guess-shell-alist-default
2. XDG commands
3. worse ones from dired-guess-shell-alist-default

Probably I'll move the worse ones to a new variable
'dired-guess-shell-alist-default-2'.