def _rename(self):
        """
        Called during a PUT request where the action specifies
        a rename operation. Returns resource URI of the renamed file.
        """
        newname = self.action['newname']
        try:
            newpath = self.fs.rename(self.fp,newname)
        except OSError:
            raise tornado.web.HTTPError(400)
        return newpath
Called during a PUT request where the action specifies
        a rename operation. Returns resource URI of the renamed file.