Returns a string containing the XML version of the Lifecycle
        configuration as defined by S3.

def to_xml(self):
        """
        Returns a string containing the XML version of the Lifecycle
        configuration as defined by S3.
        """
        s = '<LifecycleConfiguration>'
        for rule in self:
            s += rule.to_xml()
        s += '</LifecycleConfiguration>'
        return s