cmd: mkdir: complain properly if no arg given (resending)

[Frédéric Delanoy]

On Thu, Aug 4, 2011 at 00:21, Dan Kegel <dank at kegel.com> wrote:
> Also output the error to stderr, as native does.
>
> Resending to make testbot happy (first time the odd numbering confused it).

You should probably send the WCMD_output_stderr implementation as a
separate patch, since it's not mkdir-specific

Frédéric