bug#12917: 24.3.50; file-executable-p return value incorrect for directories on Windows

[Richard Copley <rcopley@gmail.com>]

On the trunk, `file-executable-p' now seems to return nil for (all?)
accessible directories. For instance, this makes most "vc-" commands fail.
This happens with Windows XP and Windows 7.

For a recipe from `emacs -Q' see the recent input and recent messages
sections below.

In GNU Emacs 24.3.50.1 (i386-mingw-nt6.1.7601)
 of 2012-11-17 on MACHINE
Bzr revision: 110920 rgm@gnu.org-20121117112058-gmycra5a7i3zkvac
Windowing system distributor `Microsoft Corp.', version 6.1.7601
Configured using:
 `configure --with-gcc (4.7) --cflags -I c:/gnuwin32/include --ldflags
 -L c:/gnuwin32/lib'

Important settings:
  value of $LANG: ENG
  locale-coding-system: cp1252
  default enable-multibyte-characters: t

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-mode: t
  mouse-wheel-mode: t
  tool-bar-mode: t
  menu-bar-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  blink-cursor-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
M-: ( f i l e - e x e c u t a b l e - p SPC " ~ " ) <return>
M-x r e p o r t - e m a c s - b u g <return>

Recent messages:
nil