bug#19045: 25.0.50; [PATCH] vc-git-print-log use --follow

[Eli Zaretskii <eliz@gnu.org>]

> From: Juri Linkov <juri@linkov.net>
> Date: Sat, 03 Feb 2018 23:59:58 +0200
> 
>  (defcustom vc-git-print-log-follow nil
> -  "If true, follow renames in Git logs for files."
> +  "If true, follow renames in Git logs for a single file."
>    :type 'boolean
>    :version "26.1")
>  
> @@ -1019,8 +1019,9 @@ If LIMIT is non-nil, show no more than this many entries."
>  	       (append
>  		'("log" "--no-color")
>                  (when (and vc-git-print-log-follow
> -                           (not (cl-some #'file-directory-p files)))
> -                  ;; "--follow" on directories is broken
> +                           (null (cdr files))
> +                           (not (file-directory-p (car files))))
> +                  ;; "--follow" on directories or multiple files is broken
>                    ;; https://debbugs.gnu.org/cgi/bugreport.cgi?bug=8756
>                    ;; https://debbugs.gnu.org/cgi/bugreport.cgi?bug=16422
>                    (list "--follow"))

What does this mean "is broken" in this context?  Is this a Git
bug/misfeature, or is that vc-git.el problem?  I cannot figure out the
answer by reading the cited bug reports.

And the doc string doesn't sound detailed enough to me, as it doesn't
tell enough about the commands that are affected.

Since this is now on the release branch, we should fix these issues
ASAP.

Thanks.