NFC: Use 'potentially unavailable' instead of 'unavailable' in the availability_versions.swift test to distinguish between test cases for types that are only available starting in a certain release versus types that are marked strictly unavailable.
NFC: Use 'potentially unavailable' instead of 'unavailable' in the availability_versions.swift test to distinguish between test cases for types that are only available starting in a certain release versus types that are marked strictly unavailable.

benlangmuir/swift,atrick/swift,benlangmuir/swift,apple/swift,atrick/swift,ahoppen/swift,atrick/swift,glessard/swift,atrick/swift,apple/swift,roambotics/swift,JGiola/swift,atrick/swift,ahoppen/swift,JGiola/swift,apple/swift,benlangmuir/swift,ahoppen/swift,roambotics/swift,glessard/swift,benlangmuir/swift,ahoppen/swift,roambotics/swift,JGiola/swift,roambotics/swift,glessard/swift,benlangmuir/swift,glessard/swift,benlangmuir/swift,ahoppen/swift,JGiola/swift,roambotics/swift,JGiola/swift,glessard/swift,JGiola/swift,apple/swift,atrick/swift,roambotics/swift,ahoppen/swift,apple/swift,glessard/swift,apple/swift