bug#28096: 25.2; c-a-p/shell/ielm: Broken directory completion for directories that contain spaces

[xristos <xristos@sdf.lonestar.org>]

emacs -Q
M-x shell
;; First create the directory structure for the test
cd /tmp/ RET
mkdir "Directory One" RET
mkdir "Directory Two" RET
;; Try to complete in shell
cd D<TAB>
;; Completes to Directory\
<TAB>
;; No match shown in *Messages* (unexpected, should list the two directories)
C-a-k
cd Directory\ O<TAB>
;; No match shown in *Messages* (unexpected, should complete Directory\ One)

;;; For ielm, we try completion inside a string

M-x ielm
"/tmp/D<TAB>
;; Completes to "/tmp/Directory
<TAB>
;; Nothing shown in *Messages*, no completion (unexpected, should list the two directories)
C-a-k
"/tmp/Directory O<TAB>
;; No match shown in *Messages*, no completion (unexpected, should complete
Directory One)


completion-at-point-functions in *ielm*:
(comint-replace-by-expanded-history ielm-complete-filename
elisp-completion-at-point)

completion-at-point-functions in *shell*:
(comint-completion-at-point t)


In GNU Emacs 25.2.1 (x86_64-apple-darwin15.6.0, NS appkit-1404.47 Version 10.11.6 (Build 15G1611))
 of 2017-08-07 built on elcapitan.internal.macports.net
Windowing system distributor 'Apple', version 10.3.1404
Configured using:
 'configure --prefix=/opt/local --without-ns --without-dbus
 --without-gconf --without-libotf --without-m17n-flt --without-gpm
 --without-gnutls --with-xml2 --with-modules --infodir
 /opt/local/share/info/emacs --with-ns CC=/usr/bin/clang 'CFLAGS=-pipe
 -Os -arch x86_64' 'LDFLAGS=-L/opt/local/lib
 -Wl,-headerpad_max_install_names -Wl,-no_pie -arch x86_64'
 CPPFLAGS=-I/opt/local/include'

Configured features:
NOTIFY ACL LIBXML2 ZLIB TOOLKIT_SCROLL_BARS NS MODULES

Important settings:
  value of $LC_ALL: en_US.UTF-8
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: IELM

Minor modes in effect:
  shell-dirtrack-mode: t
  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
  line-number-mode: t
  transient-mark-mode: t