> OK, now pushed.

More problems: XDG has much better support for media files
than dired-guess-shell-alist-default that contains many
old obsolete and random commands for media files.
OTOH, dired-guess-shell-alist-default has much better support
for non-media files than XDG and mailcap.

So currently there is no way to configure
shell-command-guess-functions to use only best commands.

When shell-command-guess-functions is configured to
'(shell-command-guess-xdg shell-command-guess-dired)
then images are opened with "xloadimage" that doesn't exist.

But when shell-command-guess-functions is configured to
'(shell-command-guess-dired shell-command-guess-xdg)
then images are opened with the existing program like "display",
but then patches can't be applied, because XDG provides
for patch files such useless commands as "more" and "less".

All this can be fixed by this patch that removes old
media commands from 'dired-guess-shell-alist-default'.
Then removed commands will not override media commands
from shell-command-guess-xdg.