bug#23813: 24.5; undo warning while find-file

[ynyaaa@gmail.com]

When `post-read-conversion' changes the buffer many times,
undo warning buffer popups.
This may occur while `find-file', even though undo info is not needed.

(let ((tmpfile "/tmp/test-hz.txt"))
  (with-temp-buffer
    (dotimes (i 100000) (insert "~{R;~}\n"))
    (write-region (point-min) (point-max) tmpfile)
    (let ((coding-system-for-read 'hz))
      (find-file tmpfile))))

Evaluating the form above, *Warnings* buffer shows this text.
  Warning (undo): Buffer `test-hz.txt' undo info was 12765470 bytes long.
  The undo info was discarded because it exceeded `undo-outer-limit'.
  
  This is normal if you executed a command that made a huge change
  to the buffer.  In that case, to prevent similar problems in the
  future, set `undo-outer-limit' to a value that is large enough to
  cover the maximum size of normal changes you expect a single
  command to make, but not so large that it might exceed the
  maximum memory allotted to Emacs.
  
  If you did not execute any such command, the situation is
  probably due to a bug and you should report it.
  
  You can disable the popping up of this buffer by adding the entry
  (undo discard-info) to the user option `warning-suppress-types',
  which is defined in the `warnings' library.




In GNU Emacs 24.5.1 (i686-pc-mingw32)
 of 2015-04-11 on LEG570
Windowing system distributor `Microsoft Corp.', version 6.0.6002
Configured using:
 `configure --prefix=/c/usr --host=i686-pc-mingw32'

Important settings:
  value of $LANG: JPN
  locale-coding-system: cp932

Major mode: Lisp Interaction

Minor modes in effect:
  tooltip-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

Recent messages:

Load-path shadows:
None found.

Features:
(shadow sort gnus-util mail-extr emacsbug message format-spec rfc822 mml
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 help-mode easymenu advice help-fns time-date
japan-util tooltip electric uniquify ediff-hook vc-hooks lisp-float-type
mwheel dos-w32 ls-lisp w32-common-fns disp-table w32-win w32-vars
tool-bar dnd fontset image regexp-opt fringe tabulated-list newcomment
lisp-mode prog-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 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 make-network-process
w32notify w32 multi-tty emacs)

Memory information:
((conses 8 78016 6918)
 (symbols 32 17691 0)
 (miscs 32 35 158)
 (strings 16 11326 4298)
 (string-bytes 1 284552)
 (vectors 8 10542)
 (vector-slots 4 465337 5130)
 (floats 8 58 110)
 (intervals 28 210 0)
 (buffers 508 13))