ls-files: --others should not say unmerged paths are unknown.

ls-files: --others should not say unmerged paths are unknown.

Jon Loeliger noticed that an unmerged path appears as
"Untracked" in git-status output, even though we show the same
path as updated/changed.  Since --others means "we have not told
git about that path", we should not show unmerged paths --
obviously, git knows about them; it just does not know what we
want to do about them yet.

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