While refactoring the options parser in bc3c79ae (fast-import: add
(non-)relative-marks feature, 2009-12-04), it was made too lenient
for options that take no argument, fix that.
Signed-off-by: NSverre Rabbelier <srabbelier@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>