What's the balance of an account?
        Aborts if its negative

def get_account_balance(self, account):
        """
        What's the balance of an account?
        Aborts if its negative
        """
        balance = namedb_get_account_balance(account)
        assert isinstance(balance, (int,long)), 'BUG: account balance of {} is {} (type {})'.format(account['address'], balance, type(balance))
        return balance