'Get the block that is linked to the given block
:param block: The block for which to get the linked block
:return: the latest block or None if it is not known'

def get_linked(self, block):

    return self._get(u'WHERE    public_key    =    ?    AND    sequence_number    =    ?    OR    link_public_key    =    ?    AND    link_sequence_number    =    ?', (buffer(block.link_public_key), block.link_sequence_number, buffer(block.public_key), block.sequence_number))
