Generate the consensus hash from the hash over the current ops, and 
        all previous required consensus hashes.

def make_snapshot_from_ops_hash( cls, record_root_hash, prev_consensus_hashes ):
        """
        Generate the consensus hash from the hash over the current ops, and 
        all previous required consensus hashes.
        """
        # mix into previous consensus hashes...
        all_hashes = prev_consensus_hashes[:] + [record_root_hash]
        all_hashes.sort()
        all_hashes_merkle_tree = MerkleTree( all_hashes )
        root_hash = all_hashes_merkle_tree.root()

        consensus_hash = StateEngine.calculate_consensus_hash( root_hash )
        return consensus_hash