tree_entry_interesting(): Make return value more specific

tree_entry_interesting() can signal to its callers not only if the given entry matches one of the specified paths, but whether all remaining paths will (or will not) match. When no paths are specified, all paths are considered interesting, so intead of returning 1 (this path is interesting) return 2 (all paths are interesting). This will allow the caller to avoid calling tree_entry_interesting() again, which theoretically should speed up tree walking. I am not able to measure any actual gains in practice, but it certainly can not hurt and seems to make the code more readable to me. Signed-off-by: Elijah Newren <newren@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>