Look up a namespace's info
        Reply information about a namespace
        Reply 404 if the namespace doesn't exist
        Reply 502 for any error in talking to the blocksatck server

def GET_namespace_info( self, path_info, namespace_id ):
        """
        Look up a namespace's info
        Reply information about a namespace
        Reply 404 if the namespace doesn't exist
        Reply 502 for any error in talking to the blocksatck server
        """
        if not check_namespace(namespace_id):
            return self._reply_json({'error': 'Invalid namespace'}, status_code=400)

        blockstackd_url = get_blockstackd_url()
        namespace_rec = blockstackd_client.get_namespace_record(namespace_id, hostport=blockstackd_url)
        if json_is_error(namespace_rec):
            # error
            status_code = namespace_rec.get('http_status', 502)
            return self._reply_json({'error': namespace_rec['error']}, status_code=status_code)

        self._reply_json(namespace_rec)
        return