bug#6165: 23.1.50; ido-mode stalls unexpectedly

[Ryan Grant <rgrant@metascopic.com>]

BUG: ido-find-file blocks all event processing while listing directory.

therefore, under certain circumstances, emacs APPEARS dead.  actually it
is just waiting while hundreds of subdirectories, on various slow NFS
mounts, are listed (/bin/ls is no faster).  "appears dead" means window
manager suggests killing it, though after directory listing completes
(in 40 seconds), it recovers.

why this matters: it's common to hit backspace one too many times while
looking for files, and in this corporate setting the behaviour is most
unexpected.

In GNU Emacs 23.1.50.1 (x86_64-pc-linux-gnu, GTK+ Version 2.18.0)
 of 2009-09-27 on crested, modified by Debian
 (emacs-snapshot package, version 1:20090909-1)
Windowing system distributor `The X.Org Foundation', version 11.0.10604000
configured using `configure  '--build' 'x86_64-linux-gnu' '--host'
'x86_64-linux-gnu' '--prefix=/usr' '--sharedstatedir=/var/lib'
'--libexecdir=/usr/lib' '--localstatedir=/var'
'--infodir=/usr/share/info' '--mandir=/usr/share/man' '--with-pop=yes'
'--enable-locallisppath=/etc/emacs-snapshot:/etc/emacs:/usr/local/share/emacs/23.1.50/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.1.50/site-lisp:/usr/share/emacs/site-lisp'
'--with-x=yes' '--with-x-toolkit=gtk' 'build_alias=x86_64-linux-gnu'
'host_alias=x86_64-linux-gnu' 'CFLAGS=-DDEBIAN
-DSITELOAD_PURESIZE_EXTRA=5000 -g -O2' 'LDFLAGS=-g -Wl,--as-needed'
'CPPFLAGS=''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_US.UTF-8
  value of $XMODIFIERS: nil
  locale-coding-system: utf-8-unix
  default enable-multibyte-characters: t

Major mode: Text

Minor modes in effect:
  which-function-mode: t
  display-time-mode: t
  show-paren-mode: t
  shell-dirtrack-mode: t
  tooltip-mode: t
  mouse-wheel-mode: t
  file-name-shadow-mode: t
  global-font-lock-mode: t
  font-lock-mode: t
  global-auto-composition-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t
  column-number-mode: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
/usr/share/emacs/23.1.50/site-lisp/cmake-data/cmake-mode hides
/usr/share/emacs/site-lisp/cmake-mode
/usr/share/emacs/23.1.50/site-lisp/debian-startup hides
/usr/share/emacs/site-lisp/debian-startup