This adds support to git-add to allow the common -- to separate
command-line options and file names. It adds documentation and a new
git-add test case as well.
[jc: this should apply to 1.2.X maintenance series, so I reworked
git-ls-files --error-unmatch test. ]
Signed-off-by: Junio C Hamano <junkio@cox.net>
