This is in preparation for more notes-related revision
command-line options.
The "suppress_default_notes" option is renamed to
"use_default_notes", and is now a tri-state with values less
than one indicating "not set". If the value is "not set",
then we show default refs if and only if no other refs were
given.
Signed-off-by: Jeff King <peff@peff.net> Signed-off-by: Junio C Hamano <gitster@pobox.com>