Add support for old Elgamal v3 key IDs

Old versions of GnuPG put Elgamal (type 16) keys inside v3 packets.
The method of getting the keyid for these keys was via a RIPE MD160
hash approach similar to the SHA-1 approach used in v4. While nothing
supports this these days there are keys in the public keyserver
network that contain this sort of data and if we don't parse the keyid
correctly we can't show things like self-sigs.