bug#12623: 24.2.50; debugger interprets selected window and current buffer as *Backtrace*

[Drew Adams]

I think this problem is new (i.e., a regression).  Perhaps it is not,
but I have not encountered/noticed it before.
 
Sometimes I cannot use the debugger at all (e.g., `debug' or
`debug-on-entry'), because the code being stepped through tests
(current-buffer) or (selected-window), and instead of the correct
buffer/window being tested, the buffer/window *Backtrace* is tested.
 
E.g., I tried `debug-on-entry quit-restore-window' and then hit `q' in
NEWS.  The first thing `quit-restore-window' does is call
`window-normalize-window', which calls `selected-window', which returns
the window for *Backtrace* (e.g. #<window 40 on *Backtrace*>), making
all such debugging useless.

In GNU Emacs 24.2.50.1 (i386-mingw-nt5.1.2600)
 of 2012-10-09 on DANI-PC
Bzr revision: 110489 monnier@iro.umontreal.ca-20121009163751-ui2zwwoaj8bqwj52
Windowing system distributor `Microsoft Corp.', version 5.1.2600
Configured using:
 `configure --with-gcc (4.7) --no-opt --enable-checking --cflags
 -I../../libs/libxpm-3.5.8/include -I../../libs/libxpm-3.5.8/src
 -I../../libs/libpng-1.4.10 -I../../libs/zlib-1.2.6
 -I../../libs/giflib-4.1.4-1/include -I../../libs/jpeg-6b-4/include
 -I../../libs/tiff-3.8.2-1/include
 -I../../libs/libxml2-2.7.8-w32-bin/include/libxml2
 -I../../libs/gnutls-3.0.16/include
 -I../../libs/libiconv-1.14-2-mingw32-dev/include'