Teach git-add and git-commit to handle filenames starting with '-'.

Recent '--' fixes to "git diff" by Linus made it possible to specify
filenames that start with '-'.  But in order to do that, you need to
be able to add and commit such file to begin with.

Teach git-add and git-commit to honor the same '--' convention.

Signed-off-by: Junio C Hamano <junkio@cox.net>

git-commit.sh

@@ -99,7 +99,7 @@ t,*)
 ,0)
 	;;
 *)
-	git-diff-files --name-only -z "$@" |
+	git-diff-files --name-only -z -- "$@" |
 	git-update-index --remove -z --stdin
 	;;
 esac || exit 1