Let OpenPGP specific commands only use OpenPGP keys.
* src/gpakeysignop.c (gpa_key_sign_operation_start): Skip non OpenPGP keys. * src/keylist.c (gpa_keylist_get_selected_keys): Add arg optional arg PROTOCOL. Adjust all callers. * src/keymanager.c (key_manager_can_sign): Cehck for OpenPGP. (key_manager_sign, key_manager_trust, key_manager_send): Act only on OpenPGP keys.