code: def already_converted(self, fpath):
          
          manifest_fpath = os.path.join(self.backend.directory,
                                        os.path.basename(fpath),
                                        'manifest.json')
          return os.path.isfile(manifest_fpath)
docs: Return true if the file already has a manifest file in the backend.
          
          :param fpath: potential path to the manifest file
          :returns: bool