bug#18514: 24.3; vc-dir sometimes guesses the wrong backend

[Barry A. Warsaw]

vc-dir sometimes guesses the wrong backend.  Here's a reproducible
example.

$ cd /tmp
$ bzr init bzrinit
$ bzr init-repo bzrinitrepo
$ git init bzrinit/gitme
$ git init bzrinitrepo/gitme

M-x vc-dir RET /tmp/bzrinit/gitme
M-x vc-dir RET /tmp/bzrinitrepo/gitme

vc-dir chooses Bzr as the backend for /tmp/bzrinit/gitme but git as the
backend for /tmp/bzrinitrepo/gitme.  In both cases, git should have been
chosen.

In GNU Emacs 24.3.1 (x86_64-pc-linux-gnu, GTK+ Version 3.10.9)
 of 2014-06-06 on brownie, modified by Debian
Windowing system distributor `The X.Org Foundation', version 11.0.11600000
System Description:     Ubuntu Utopic Unicorn (development branch)

Configured using:
 `configure '--build' 'x86_64-linux-gnu' '--build' 'x86_64-linux-gnu'
 '--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib'
 '--localstatedir=/var/lib' '--infodir=/usr/share/info'
 '--mandir=/usr/share/man' '--with-pop=yes'
 
'--enable-locallisppath=/etc/emacs24:/etc/emacs:/usr/local/share/emacs/24.3/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/24.3/site-lisp:/usr/share/emacs/site-lisp'
 '--with-crt-dir=/usr/lib/x86_64-linux-gnu' '--with-x=yes'
 '--with-x-toolkit=gtk3' '--with-toolkit-scroll-bars'
 'build_alias=x86_64-linux-gnu' 'CFLAGS=-g -O2 -fstack-protector
 --param=ssp-buffer-size=4 -Wformat -Werror=format-security -Wall'
 'LDFLAGS=-Wl,-Bsymbolic-functions -Wl,-z,relro'
 'CPPFLAGS=-D_FORTIFY_SOURCE=2''

Important settings:
  value of $LC_COLLATE: en_US.UTF-8
  value of $LC_CTYPE: en_US.UTF-8
  value of $LC_MESSAGES: en_US.UTF-8
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: @im=ibus
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: VC dir

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
  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Recent input:
<help-echo> <help-echo> <help-echo> <escape> x v c 
- d i r <return> b z r i n i <tab> / g i <tab> <return> 
<escape> x v c - d i r <return> <backspace> <backspace> 
<backspace> <backspace> <backspace> <backspace> <backspace> 
r e <tab> g i t m e <tab> <return> <escape> x r e p 
o r t - e m <tab> <return>

Recent messages:
For information about GNU Emacs and the GNU system, type C-h C-a.
You can run the command `vc-dir' with C-x v d
error in process sentinel: vc-dir-update: Wrong type argument: arrayp, nil
error in process sentinel: Wrong type argument: arrayp, nil
You can run the command `vc-dir' with C-x v d

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
easymenu mml-sec mm-decode mm-bodies mm-encode mail-parse rfc2231
mailabbrev gmm-utils mailheader sendmail rfc2047 rfc2045 ietf-drums
mm-util mail-prsvr mail-utils vc-git vc-bzr vc-sccs vc-svn vc-cvs vc-rcs
vc-dir ewoc vc vc-dispatcher time-date tooltip ediff-hook vc-hooks
lisp-float-type mwheel x-win x-dnd tool-bar dnd fontset image regexp-opt
fringe tabulated-list newcomment lisp-mode register page menu-bar
rfn-eshadow timer select scroll-bar mouse jit-lock font-lock syntax
facemenu font-core frame cham georgian utf-8-lang misc-lang vietnamese
tibetan thai tai-viet lao korean japanese hebrew greek romanian slovak
czech european ethiopic indian cyrillic chinese case-table epa-hook
jka-cmpr-hook help simple abbrev minibuffer loaddefs button faces
cus-face macroexp files text-properties overlay sha1 md5 base64 format
env code-pages mule custom widget hashtable-print-readable backquote
make-network-process dbusbind dynamic-setting system-font-setting
font-render-setting move-toolbar gtk x-toolkit x multi-tty emacs)