bug#8789: 23.3; debug backtrace buffer changes window on step-through

["Drew Adams" <drew.adams@oracle.com>]

I'm guessing, but I do not know for sure, that it is the change you made for
this bug that has now broken the debugger for me.

For me, *Backtrace* is a special-display buffer, so it is shown in its own,
special-display frame.

In this build, things are not broken (still OK):

In GNU Emacs 24.2.50.1 (i386-mingw-nt5.1.2600)
 of 2012-09-02 on MARVIN
Bzr revision: 109861 eggert@cs.ucla.edu-20120902171035-7mzihil3xd6bjfiy
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'

And in this build, things are broken:

In GNU Emacs 24.2.50.1 (i386-mingw-nt5.1.2600)
 of 2012-09-17 on MARVIN
Bzr revision: 110062 cyd@gnu.org-20120917054104-r93rtwkrtva73ewe
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.7) --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'

What is broken is this:

Before, the same frame (seemingly) existed throughout.  I could hit `d' any
number of times, and everything was smooth.  I could expand the frame size or
reposition it, and it stayed wherever I put it.

Now, it appears that each time I hit `d' the frame is deleted and a new frame is
created to replace it.  And it is always re-created with the same, default size
and position (top left of screen).

This is horrible.  Not only does the re-creation produce a tremendous
blink/flash, but the repositioning and resizing back to the default position and
size are intolerable.

I cannot see anything useful in the buffer - I need to stretch the frame out
again after each `d' to see anything wide.

And I need to reposition the frame to the right (for example) after each `d', if
I have another frame at the left that I want to continue to see (e.g. a frame
showing the source code, or *Completions*).

If you prefer this as a separate bug report, feel free to copy the above into a
new bug - you have all of the info.  This is with my own setup, which Martin is
pretty familiar with: non-nil popup-frames etc.

For me, this change is a horrible regression - makes the debugger unusable.