Relocation: Document empty directory issue

            // TODO(dauer) process output

            GKFS_DATA->storage()->remove_chunk(file_path, chunk_id);

            // FIXME This can leave behind empty directories, even when the

            // whole file is delete later. Three possibilities:

            // 1) Clean them up, but make sure this doesn't break another thread

            // creating a new chunk in this directory at the same time.

            // 2) Switch to a flat namespace without directories

            // 3) Ignore and waste some inodes

            if(HG_SUCCESS != gkfs::rpc::margo_client_cleanup(

                                     &handle, &out, &mid, &host_addr, &bulk)) {

                cout << "Error during margo cleanup.\n";