bug#13661: 24.3.50; shell-command fails with w32-downcase-file-names

[Eli Zaretskii]

> From: <rcopley@gmail.com>
> Date: Sat, 9 Feb 2013 14:35:15 +0000
> 
> The `shell-command' function fails if `w32-downcase-file-names' is true.
> 
> 
> Recipe from -Q:
> M-: (setq SPC w32-downcase-file-names SPC t) RET
> 
> M-! dir <return>
> 
> 
> Result:
> (Shell command failed with error)
> shell-command-on-region: File exists: 
> c:/users/buster/appdata/local/temp/emxxxxxx

Damn that w32-downcase-file-names option!  Why are people still using
it in the year 2013??

Thanks; fixed in revision 111711.