Write the Media RSS Feed's XML representation to the given file.

def write_xml(self, outfile, encoding="UTF-8"):
        """Write the Media RSS Feed's XML representation to the given file."""
        # we add the media namespace if we see any media items
        if any([key for item in self.items for key in vars(item) if
                key.startswith('media_') and getattr(item, key)]):
            self.rss_attrs["xmlns:media"] = "http://search.yahoo.com/mrss/"
        self.generator = _generator_name
        super(MediaRSS2, self).write_xml(outfile, encoding)