daemon: detect and reject too-long paths

daemon: detect and reject too-long paths

When we are checking the path via path_ok(), we use some
fixed PATH_MAX buffers. We write into them via snprintf(),
so there's no possibility of overflow, but it does mean we
may silently truncate the path, leading to potentially
confusing errors when the partial path does not exist.

We're better off to reject the path explicitly.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>