Flatten names of files and create temporary file names.

def _flatten_plus_safe(data_and_files):
    """Flatten names of files and create temporary file names.
    """
    data, rollback_files = _normalize_args(data_and_files)
    with tx_tmpdir(data) as tmpdir:
        tx_files = [os.path.join(tmpdir, os.path.basename(f))
                    for f in rollback_files]
        yield tx_files, rollback_files