Adding verify_prehashed_strict()

[orthecreedence]

Combines verify_prehashed and verify_strict to allow strict verification with prehashed values.

Wrote an integration test (repudiation_prehash) however it fails intermittently as the verify_prehashed() call sometimes fails. I will need guidance on why because I'm not familiar with the inner workings of the verification, I really just kind of merged the prehashed/strict functions together.