revision.c: make --no-notes reset --notes list

revision.c: make --no-notes reset --notes list

With most command line options, later instances of an option
override earlier ones. With cumulative options like
"--notes", however, there is no way to say "forget the
--notes I gave you before".

Let's have --no-notes trigger this forgetting, so that:

  git log --notes=foo --no-notes --notes=bar

will show only the "bar" notes.

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