'Add a new L{HashedEntry} to the key database.
Note that you still need to call L{KnownHostsFile.save} if you wish
these changes to be persisted.
@param hostname: A hostname or IP address literal to associate with the
new entry.
@type hostname: L{bytes}
@param key: The public key to associate with the new entry.
@type key: L{Key}
@return: The L{HashedEntry} that was added.
@rtype: L{HashedEntry}'

def addHostKey(self, hostname, key):

    salt = secureRandom(20)
    keyType = key.sshType()
    entry = HashedEntry(salt, _hmacedString(salt, hostname), keyType, key, None)
    self._added.append(entry)
    return entry
