Process all keys and signatures we find

Process all keys and signatures we find

- We still can't store more than one signature / key at a time, but
  since we can easily *process* them without trashing already stored
  values, lets do so to avoid returning errors from legal packets.
  Also pay attention to only store data matching our expected type,
  ie dont store signature data into pubkey parameters and vice versa.
- This mostly affects pubkey packets which can have more than one
  key present and which (can) also carry certification signature
  which we currently do not handle properly at all.