"git status" and "git commit" read .git/config and .gitmodules before
parsing options, but there is no reason to access a repository at all
when the caller just wanted to know what arguments are accepted.

[jn: rewrote the log message and added test]
Signed-off-by: NNguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: NJonathan Nieder <jrnieder@gmail.com>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>