MS-Windows build now supports symlinks on Vista and later

[Eli Zaretskii]

Beginning with trunk revision 109416, the MS-Windows build of Emacs
supports symbolic links when the OS and the underlying filesystem do
(NTFS on Windows Vista and later).  This includes both creation and
resolution of symlinks.

Note that MS, in their great wisdom (yeah, right) decided to make
symlink creation a privileged operation (allegedly, symlinks can
circumvent NTFS file security).  So you will need to add that
privilege to your user profile (via Local Policies), and if you are a
member of the Administrators group, you will have to run Emacs "as
administrator" to be able to create symlinks.  Or just disable the
UAC.  (You get the same behavior and limitations with mklink, a
utility included with Windows for creating symlinks, so Emacs's
behavior is not an exception here, but rather the rule.  If someone
knows how to work around these misfeatures, please speak up.)

Following a symlink does not require any special privileges.  And
there are already symlinks on every Windows 7 box, even if you didn't
create any.  Just look around in system directories on the system
drive.

I've tested this with make-symbolic-link and file-symlink-p
primitives, and also with file-attributes,
directory-files-and-attributes and Dired.  However, much more testing
is needed, so please exercise these features as much as you can.

As part of these changes, the emulation of 'stat' was reworked, and as
result it should become faster.  This also means that exciting new
bugs may have been introduced, so please be alert to any unusual
behavior related to accessing files and their attributes, even if you
are on a system that does not support symlinks.

Enjoy.