code: func bucketizedKey(bucketID [4]byte, key []byte) []byte {
  	// The serialized block index key format is:
  	//   <bucketid><key>
  	bKey := make([]byte, 4+len(key))
  	copy(bKey, bucketID[:])
  	copy(bKey[4:], key)
  	return bKey
  }
docs: // bucketizedKey returns the actual key to use for storing and retrieving a key
  // for the provided bucket ID.  This is required because bucketizing is handled
  // through the use of a unique prefix per bucket.