libkeyringctl/keyring.py:
Simplify `convert_certificate()` by splitting out the conversion of
signature packets to `convert_signature_packet()` and the persistence of
packet material to `persist_key_material()`.
Add `convert_pubkey_signature_packet()`,
`convert_uid_signature_packet()` and
`convert_subkey_signature_packet()` to deal with the conversion of
public key signatures, UID signatures and subkey signatures
(respectively).
tests/test_keyring.py:
Add tests for `convert_certificate()`, `convert_signature_packet()`,
`convert_{pubkey,uid,subkey}_signature_packet()` and
`persist_subkey_revocations()`.
e43a28f4a7