bug#7546: 23.2; [dired] leading spaces in directory names

[Chong Yidong]

Glenn Morris <rgm@gnu.org> writes:

> To me, it makes most sense to test what options ls actually supports:
>
> (with-temp-buffer
>  (call-process "ls" nil t nil "--help")
>  (and (re-search-backward "--dired" nil t) t))

It's better to check the exit code of `ls --dired'.  I've committed such
a fix to the trunk.