win32mbcs: allow win32mbcs extension to be enabled on cygwin platform this patch allows win32mbcs extension to be enabled on cygwin platform for problematic character encodings. on recent cygwin platform, even though "os.path.supports_unicode_filenames" is False, "os.listdir()" and other path manipulation functions can return the result correctly decoded in unicode for invocations with unicode arguments, if locale is configured properly. existing code to check "os.path.supports_unicode_filenames" is kept to prevent win32mbcs from being enabled on unexpected platform.