bug#28529: 26.0.60; Dired recursive copy fails

[Richard Copley <rcopley@gmail.com>]

* Create directories ./x/, ./x/a/ and ./y/
* Run "emacs -Q ."
* In Dired, use C (dired-do-copy) to copy x/ into y/

Expected: succeeds
Actual: fails with error:
Copy ‘c:/temp/test/x’ to ‘c:/temp/test/y/x’ failed:
(file-already-exists File exists c:/temp/test/y/x)

In GNU Emacs 26.0.60 (build 3, x86_64-w64-mingw32)
 of 2017-09-20 built on XXX
Repository revision: 26a27b6d095344cceb7d9477d9d8fdbe378a2b75
Windowing system distributor 'Microsoft Corp.', version 6.1.7601
Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
Copy ‘c:/temp/test/x’ to ‘c:/temp/test/y/x’ failed:
(file-already-exists File exists c:/temp/test/y/x)


Configured using:
 'configure --config-cache --with-modules --without-pop 'CFLAGS=-O3
 -ggdb3''

Configured features:
XPM JPEG TIFF GIF PNG RSVG SOUND NOTIFY ACL GNUTLS LIBXML2 ZLIB
TOOLKIT_SCROLL_BARS MODULES

Important settings:
  value of $LANG: ENG
  locale-coding-system: cp1252

Major mode: Dired by name

Minor modes in effect:
  tooltip-mode: t
  global-eldoc-mode: t
  electric-indent-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
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message subr-x puny seq byte-opt gv
bytecomp byte-compile cconv format-spec rfc822 mml easymenu mml-sec
password-cache epa derived epg epg-config gnus-util rmail rmail-loaddefs
mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils
mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils dired-aux cl-loaddefs cl-lib dired dired-loaddefs elec-pair
time-date mule-util tooltip eldoc electric uniquify ediff-hook vc-hooks
lisp-float-type mwheel dos-w32 ls-lisp disp-table term/w32-win w32-win
w32-vars term/common-win tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page menu-bar rfn-eshadow isearch timer select
scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame cl-generic cham georgian utf-8-lang misc-lang
vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms cp51932
hebrew greek romanian slovak czech european ethiopic indian cyrillic
chinese composite charscript charprop case-table epa-hook jka-cmpr-hook
help simple abbrev obarray minibuffer cl-preloaded nadvice loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote w32notify w32 multi-tty make-network-process emacs)

Memory information:
((conses 16 99152 6641)
 (symbols 56 20218 1)
 (miscs 48 47 108)
 (strings 32 29840 1501)
 (string-bytes 1 754128)
 (vectors 16 14980)
 (vector-slots 8 489750 6675)
 (floats 8 50 66)
 (intervals 56 297 35)
 (buffers 992 13))