Get two consecutive account states---the one at (block_id, vtxindex), and the one prior.

def get_account_delta(self, address, token_type, block_id, vtxindex):
        """
        Get two consecutive account states---the one at (block_id, vtxindex), and the one prior.
        """
        cur = self.db.cursor()
        return namedb_get_account_delta(cur, address, token_type, block_id, vtxindex)