Signature support: separate the checkin of trust and digest.
Signature support: separate the checkin of trust and digest.

The openssl function we were using checked both trust and the
digest. Annoyingly, it checked trust first, so some trickery
had to be used to check the digest for self-signed certificates.
Now we make use of parts of the functions we were calling to
provide the two parts of the check as separate functions.

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