bug#12071: 24.1.50; (pp-display-expression): user-error: No undo information in this buffer

[Jambunathan K]

It would be quite useful if one can actually *undo* edits in the pp
buffer.

Background:

I am examining a deeply nested list as shown below.

  (pp-display-expression deeply-nested-list "*deeply-nested-list*")


Often times I find myself editing/re-adjusting the pp display buffer to
make sense out of what is in there.  I also find myself undoing edits to
that buffer.  This is when the following user-error is thrown.

  user-error: No undo information in this buffer

-----------------------------------------------

In GNU Emacs 24.1.50.1 (i386-mingw-nt5.1.2600)
 of 2012-07-23 on MARVIN
Bzr revision: 109189 
vincentb1@users.sourceforge.net-20120722211412-mnq2ih82me0bpuhx
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.6) --no-opt --enable-checking --cflags
 -ID:/devel/emacs/libs/libXpm-3.5.8/include
 -ID:/devel/emacs/libs/libXpm-3.5.8/src
 -ID:/devel/emacs/libs/libpng-dev_1.4.3-1/include
 -ID:/devel/emacs/libs/zlib-dev_1.2.5-2/include
 -ID:/devel/emacs/libs/giflib-4.1.4-1/include
 -ID:/devel/emacs/libs/jpeg-6b-4/include
 -ID:/devel/emacs/libs/tiff-3.8.2-1/include
 -ID:/devel/emacs/libs/gnutls-3.0.9/include
 -ID:/devel/emacs/libs/libiconv-1.13.1-1-dev/include
 -ID:/devel/emacs/libs/libxml2-2.7.8/include/libxml2'

Important settings:
  value of $EMACSDATA: C:/Program Files/emacs-24.1.50/etc
  value of $EMACSDOC: C:/Program Files/emacs-24.1.50/etc
  value of $EMACSLOADPATH: C:/Program Files/emacs-24.1.50/site-lisp;C:/Program 
Files/emacs-24.1.50/../site-lisp;C:/Program Files/emacs-24.1.50/lisp;C:/Program 
Files/emacs-24.1.50/leim
  value of $EMACSPATH: C:/Program Files/emacs-24.1.50/bin
  value of $LANG: ENG
  locale-coding-system: cp1252
  default enable-multibyte-characters: t