bug#11067: 24.0.94.1; diff-buffer-with-file

[Arni Magnusson <arnima@hafro.is>]

I'm running Emacs 24.0.94.1 alpha,

http://alpha.gnu.org/gnu/emacs/windows/emacs-20120319-r107630-bin-i386.zip

and `diff-buffer-with-file' is not working like it did in Emacs 23.4.1

1. Start emacs -Q
2. Set `diff-command' to "winmerge" and `diff-switches' to nil
3. Open a file, say c:/gnu/emacs/BUGS, make some changes without saving
4. M-x diff-buffer-with-file

Emacs 23.4.1 performs this task very nicely, but Emacs 24.0.94.1 alpha 
provides the external program with args that cannot be compared:

   c:\gnu\emacs\-L
   c:\gnu\emacs\BUGS

Examining the Emacs *Diff* buffer provides some insights. In Emacs 23.4.1 
it contains

   winmerge "c:/gnu/emacs/BUGS" "c:/Temp/buffer-content-3436L7C"

which looks sensible, but in Emacs 24.0.94.1 alpha it the *Diff* buffer 
contains

   winmerge "-L" "c:/gnu/emacs/BUGS" "-L" "#<buffer BUGS>" 
"c:/gnu/emacs/BUGS" "c:/Temp/buffer-content-2640boz"

which looks like 6 args instead of 2, including some "-L" options (even 
after specifically disabling all diff switches) and "#<buffer BUGS>" 
(probably of no use to an external program).

To me, it looks like version 24.0.94.1 of `diff-buffer-with-file' in 
diff.el should try harder to mimic the behavior of version 23.4.1 in 
files.el.

Many thanks,

Arni