gpg: Make rfc4880bis the default.

* g10/gpg.c (set_compliance_option, main): Change CO_GNUPG to include
rfc4880bis features.
(main): Change rfc4880bis warning to a note.

Note that the default is CO_GNUPG and not CO_OPENPGP. CO_OPENPGP does
not include rfc4880bis yet and has a couple of things we don't like,
like --allow-non-selfsigned-uids.

• Signed-off-by: Werner Koch <wk@gnupg.org>