bug#13539: Use fdopendir, fstatat and readlinkat, for efficiency.

[Eli Zaretskii]

> Date: Tue, 29 Jan 2013 16:56:37 -0800
> From: Paul Eggert <eggert@cs.ucla.edu>
> CC: 13539@debbugs.gnu.org
> 
> But there's another approach: simply set fd = 0, and use 
> dir_pathname inside w32.c.  This should be good enough for what Emacs needs.
> Revised patch attached.

Works for me, thanks.