Generator. Yields the next rotated file as a tuple:
    (path, rotation_id)

def _rotated_files(path):
    """Generator. Yields the next rotated file as a tuple:
    (path, rotation_id)
    """
    for globbed_path in iglob(path + FILE_NAME_GLOB):
        match = re.search(FILE_NAME_REGEX, globbed_path)
        if match:
            yield globbed_path, int(match.group('rotation_id'))