As a short option, we cannot handle negation. Thus a callback
handling "unset" is overkill, and we can just use OPT_SET_INT
instead to handle setting the option.
Anybody who adds "--nul" synonym to this later would need to be
careful not to break "--no-nul", which should mean that lines are
terminated with LF at the end.
Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>