Document user argument
AppleDoc +ck2_credentialForKnownHostWithPersistence:
Document CK2AuthenticationMethodHostFingerprint
AppleDoc -ck2_knownHostMatch
Bump +ck2_protectionSpaceWithHost:knownHostMatch: down

It's unimportant to typical clients
AppleDoc +ck2_protectionSpaceWithHost:knownHostMatch: