* keygen.c (write_selfsigs): Rename from write_selfsig.  Write the same
selfsig into both the pk and sk, so that someone importing their sk (which
will get an autoconvert to the pk) won't end up with two selfsigs.
(do_generate_keypair): Call it from here.
* parse-packet.c (can_handle_critical_notation): New.  Check for
particular notation tags that we will accept when critical. Currently,
that's only preferred-email-encoding@pgp.com, since we know how to handle
it (pass it through to a mail program). (can_handle_critical): Call it
from here. (parse_one_sig_subpkt): Sanity check that notations are
well-formed in that the internal lengths add up to the size of the
subpacket.