Given a name and block number, determine if it is expired at that block.
        * names in revealed but not ready namespaces are never expired, unless the namespace itself is expired;
        * names in ready namespaces expire once max(ready_block, renew_block) + lifetime blocks passes

        Return True if so
        Return False if not, or if the name doesn't exist

def is_name_expired( self, name, block_number ):
        """
        Given a name and block number, determine if it is expired at that block.
        * names in revealed but not ready namespaces are never expired, unless the namespace itself is expired;
        * names in ready namespaces expire once max(ready_block, renew_block) + lifetime blocks passes

        Return True if so
        Return False if not, or if the name doesn't exist
        """
        cur = self.db.cursor()
        return namedb_get_name( cur, name, block_number ) is None