Add "--" after <commit-ish> or <tree-ish> argument to clearly mark it
as <commit-ish> or <tree-ish> and not pathspec, securing against refs
with the same names as files or directories in [live] repository.

Some wrapping to reduce line length as well.

[jc: with "oops, ls-tree does not want --" fix-up manually applied.]
Signed-off-by: NJakub Narebski <jnareb@gmail.com>
Signed-off-by: NJunio C Hamano <junkio@cox.net>