Called during a PUT request where the action specifies
        a move operation. Returns resource URI of the destination file.

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