The full block with all 5 signatures remains, but this allows passing
individual signatures through the GPG verification APIs. The split was
done with `gpgsplit`, and looking at the output of `gpg --list-packets`
of the split and unsplit files appears correct.
Wrappers a referenced gpgme_verify_result_t so detailed verify results
can be examined independently of executing a verify operation.
_ostree_gpg_verifier_check_signature() now returns this object instead
of a single valid/invalid boolean, but the idea is for OstreeRepo to also
return this object for commit signature verification so it can be utilized
at the CLI layer (and possibly by other programs).
Dan Nicholson
Matthew Barnes