with this patch, setup.py creates windows .bat files
instead of *nix shell scripts when 'bdist_wininst' or
'bdist --formats=wininst' is run on non-windows platform.

'bdist' command checks only the first of specified
formats, and makes windows scripts if it is 'wininst'
or if current (build) platform is 'win32'.  otherwise
it creates shell scripts.

'bdist_wininst' always creates windows files.