git-status older than v1.7.0-rc0~137^2~17 used to take the same options
as git-commit. So reimplement the needed logic using plumbing. An
alternative would be using git commit --dry-run.
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de> Tested-by: James Vega <jamessan@debian.org> Closes: http://bugs.debian.org/581582