bug#2445: 23.0.90; file name completion GCs a lot

When I type C-x C-f xmail/foox TAB, where xmail contains 800 files
and none of them starts with foox, it takes a few seconds (including
3 GCs) before telling me it can't be found.
Here's output from xbacktrace:

    "file-name-completion" (0x7fbe23e4)
    "completion--file-name-table" (0x7fbe26c4)
    "complete-with-action" (0x7fbe29a4)
    0x87978c PVEC_COMPILED
    "byte-code" (0x7fbe2f14)
    "completion--some" (0x7fbe33b4)
    0x8797dc PVEC_COMPILED
    "apply" (0x7fbe3710)
    "read-file-name-internal" (0x7fbe38f4)
    "try-completion" (0x7fbe3a74)
    "completion-pcm--find-all-completions" (0x7fbe3f2c)
    "completion-pcm-try-completion" (0x7fbe4214)
    0x879d04 PVEC_COMPILED
    "byte-code" (0x7fbe4784)
    "completion--some" (0x7fbe4c24)
    "completion-try-completion" (0x7fbe4f04)
    "completion--do-completion" (0x7fbe51f4)
    "minibuffer-complete" (0x7fbe550c)
    "call-interactively" (0x7fbe5764)
    "completing-read" (0x7fbe5ebc)
    "read-file-name" (0x7fbe61ac)
    "find-file-read-args" (0x7fbe648c)
    "byte-code" (0x7fbe671c)
    "call-interactively" (0x7fbe69c4)

I think that is because of the partial completion feature
that is now enabled by default and was not before.

I don't notice (or mind) the feature itself.  But the delay
is a real pain whenever I make a typo in these names.
I think the feature should be disabled by default
if it can't be made fast enough to run in half a second.

This is on the Lemote Yeelong mini-laptop.



In GNU Emacs 23.0.90.4 (mipsel-unknown-linux-gnu, GTK+ Version 2.12.11)
 of 2009-02-23 on lemote-yeeloong
configured using `configure  'CFLAGS=-O0 -g -Wno-pointer-sign' 'mipsel-unknown-linux-gnu' 'build_alias=mipsel-unknown-linux-gnu' 'host_alias=mipsel-unknown-linux-gnu' 'target_alias=mipsel-unknown-linux-gnu''

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: Emacs-Lisp

Minor modes in effect:
  gpm-mouse-mode: t
  tooltip-mode: t
  tool-bar-mode: t
  menu-bar-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
  line-number-mode: t
  transient-mark-mode: t
  abbrev-mode: t

Recent input:
C-x b RET C-z o x m a i l / f o o x TAB C-z C-g o x 
a i DEL DEL m a i l / f o o x TAB C-g C-z C-x C-g ESC 
x C-g C-h f r e o DEL p o r t - f i l e - ESC DEL ESC 
DEL r e a d - f i e - DEL DEL l e - n a m e - i n t 
e r n a l RET C-x o TAB RET C-x 1 ESC x r e p o r t 
SPC e m a s DEL c s SPC b u g RET

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