support long keyid and fingerprint in gpgv's GOODSIG

support long keyid and fingerprint in gpgv's GOODSIG

In gpgv1 GOODSIG (and the other messages of status-fd) are documented as
sending the long keyid. In gpgv2 it is documented to be either long
keyid or the fingerprint. At the moment it is still the long keyid, but
the documentation hints at the possibility of changing this.

We care about this for Signed-By support as we detect this way if the
right fingerprint has signed this file (or not). The check itself is
done via VALIDSIG which always is a fingerprint, but there must also be
a GOODSIG (as expired sigs are valid, too) found to be accepted which
wouldn't be found in the fingerprint-case and the signature hence
refused.