po: Fix the French DEL, ERASE, RD and RMDIR usage messages.

[Frédéric Delanoy]

On Fri, Jul 12, 2013 at 12:34 PM, Francois Gouget <fgouget at free.fr> wrote:
>  msgid "DEL <filename> deletes a file or set of files.\n"
> -msgstr "DEL <fichiers> efface un fichier ou un groupe de fichiers.\n"
> +msgstr "DEL <fichier> efface un fichier ou un groupe de fichiers.\n"

"fichiers" indicate it can be any number of files, replacing by the
singular form doesn't (one may think only one file is deletable per
command)

If you absolutely want the same singular ou plural form, the English
msgid it what should be changed instead IMO

Same remark for your ERASE diff hunk.

Regards,

Frédéric