Keep track of each file in list file_names.

    Tracking does not create or delete the actual file, it only tells the
    version control system whether to maintain versions (to keep track) of
    the file.

def track(context, file_names):
    """Keep track of each file in list file_names.

    Tracking does not create or delete the actual file, it only tells the
    version control system whether to maintain versions (to keep track) of
    the file.
    """
    context.obj.find_repo_type()
    for fn in file_names:
        context.obj.call([context.obj.vc_name, 'add', fn])