Display distinct errors for various problematic CRL/MFT situationships

Display distinct errors for various problematic CRL/MFT situationships

RFC 6487 section 8 specifies only a single CRL is issued at a time, so
error when multiple .crl files are listed in a Manifest's FileList.

The CRLDP extension identifies the location of the CRL, so the CRL's
filename must match the CA's CRLDP's 'rsync://' entry, error if that
isn't the case. (RFC 6486 section 4.8.6)

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