bug#25942: 26.0.50; dired-mark-extension prepend '.' to suffix if not present

[Eli Zaretskii]

> From: Tino Calancha <tino.calancha@gmail.com>
> Date: Mon, 27 Mar 2017 10:30:26 +0900 (JST)
> Cc: 25942@debbugs.gnu.org, Tino Calancha <tino.calancha@gmail.com>
> 
> The problem is that this command has a concept of 'extension' different 
> than the two other functions mentioned above.

Then how about providing a new command, named dired-mark-suffix or
somesuch, which would work like dired-mark-extension does now?  Or
maybe have an optional argument, activated by prefix arg to
dired-mark-extension, to do that?  That would leave users a way to get
back the old behavior, if they want.