// directory, which will look something like
	// "$GOROOT/src/mime/multipart" or "$GOPATH/src/golang.org/x/mobile".
	// We extract everything after the $GOROOT or $GOPATH to run on the
	// same relative directory on the target device.
	importPath, isStd, modPath, modDir, err := pkgPath()
	if err != nil {
		return 0, err
	}
	var deviceCwd string
	if isStd {

	}
	x.versions, buf, err = msgp.ReadIntBytes(buf)
	if err != nil {
		return x, buf, err
	}
	if x.versions < 0 {
		return x, buf, fmt.Errorf("decodeXLHeaders: Negative version count %d", x.versions)
	}
	return x, buf, nil
}

// decodeVersions will decode a number of versions from a buffer
// and perform a callback for each version in order, newest first.