Close all open files (so that we can open more).

def close_all_files(self):
        """Close all open files (so that we can open more)."""
        while len(self.open_file_infos) > 0:
            file_info = self.open_file_infos.pop(0)
            file_info.file_handle.close()
            file_info.file_handle = None
            self.closed_file_infos.append(file_info)
        self.can_open_more_files = True