This drops the magic number for the fixed-size argv arrays,
so we do not have to wonder if we are overflowing it. We can
also drop some confusing sha1_to_hex memory allocation
(which seems to predate the ring of buffers allowing
multiple calls), and get rid of an unchecked sprintf call.
Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>