Create a ZODB connection pool from the *app* configuration.

def create_db(self, app):
        """Create a ZODB connection pool from the *app* configuration."""
        assert 'ZODB_STORAGE' in app.config, \
               'ZODB_STORAGE not configured'
        storage = app.config['ZODB_STORAGE']
        if isinstance(storage, basestring):
            factory, dbargs = zodburi.resolve_uri(storage)
        elif isinstance(storage, tuple):
            factory, dbargs = storage
        else:
            factory, dbargs = storage, {}
        return DB(factory(), **dbargs)