// whether it's a DOS path reasonably reliably by looking for
	// a drive letter or UNC path.
	drive, dirname := splitDrive(dirname)
	if drive == "" {
		// UNIX-style path.
		return path.Join(dirname, filename)
	}
	// DOS-style path.
	drive2, filename := splitDrive(filename)
	if drive2 != "" {
		if !strings.EqualFold(drive, drive2) {
			// Different drives. There's not much we can