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

[Tino Calancha <tino.calancha@gmail.com>]

On Mon, 27 Mar 2017, Tino Calancha wrote:

>
>
> On Mon, 27 Mar 2017, Juri Linkov wrote:
>
>>> emacs -Q /tmp
>>> 
>>> (require 'dired-x)
>>> (require 'ert)
>>> ;; Evaluate following sexp:
>>> (let ((dirs '("Public" "Music"))
>>>       (files '(".bashrc" "bar.c" "foo.c"))
>>>       (dir (make-temp-file "Bug25942" 'dir)))
>>>   (unwind-protect
>>>       (progn
>>>         (dolist (d dirs)
>>>           (make-directory (expand-file-name d dir)))
>>>         (dolist (f files)
>>>           (write-region nil nil (expand-file-name f dir)))
>>>         (dired dir)
>>>         (dired-mark-extension "c")
>>>         (should (= 2 (length (dired-get-marked-files)))))
>>>     (delete-directory dir 'recursive)))
>>> 
>>> IMO, in this example looks better if just those files ending with
>>> '.c' are marked i.e., to not mark 'Public' or 'Music'.
>> 
>> Is this a backward-compatible change?
> Yes, it is; but it makes a better global picture when we consider
> this function together with `file-name-extension' and
> `file-name-sans-extension' (More below).
Sorry, i meant 'No, it isn't; but it makes a better ...'