Rationale for (file-name-as-directory "") => "/"?

[Noah Friedman <friedman@splode.com>]

>Subject says all.  I know Emacs behaves that way, but the XEmacs
>developers are wondering just the same.
>
>It seems "./" would be a more reasonable choice, no?  (I would
>personally have it raise an error, but that's just me ...)

Unix file name semantics being what they are, and since
file-name-as-directory interprets other arguments relative to the current
working directory, I think "./" is probably the correct thing for it to do.