func HashFileNode(n *FileNodeProto) []byte {
	hash := sha256.New()
	// Compute n.Hash by concatenating all BlockRef hashes in n.FileNode.
	for _, object := range n.Objects {
		hash.Write([]byte(object.Hash))
	}
	return hash.Sum(nil)
}
func HashFileNode(n *FileNodeProto) []byte {
	hash := sha256.New()
	// Compute n.Hash by concatenating all BlockRef hashes in n.FileNode.
	for _, object := range n.Objects {
		hash.Write([]byte(object.Hash))
	}
	return hash.Sum(nil)
}
// HashFileNode computes the hash of 'node' and writes
// the result into node.Hash. Exported so that PFS
// can compute the hash of synthetic nodes (filenodes
// that inherit headers/footers from their parent
// directories)