Directive for registering a file-system based repository.

def filesystem_repository(_context, name=None, make_default=False,
                          aggregate_class=None, repository_class=None,
                          directory=None, content_type=None):
    """
    Directive for registering a file-system based repository.
    """
    cnf = {}
    if not directory is None:
        cnf['directory'] = directory
    if not content_type is None:
        cnf['content_type'] = content_type
    _repository(_context, name, make_default,
                aggregate_class, repository_class,
                REPOSITORY_TYPES.FILE_SYSTEM, 'add_filesystem_repository',
                cnf)