Add hash checking for external sites.
Add hash checking for external sites.

The ISO links rely heavily on hashes, so check them automatically.

AppliedLogicSystems/ALSProlog,AppliedLogicSystems/ALSProlog,AppliedLogicSystems/ALSProlog,AppliedLogicSystems/ALSProlog,AppliedLogicSystems/ALSProlog,AppliedLogicSystems/ALSProlog,AppliedLogicSystems/ALSProlog,AppliedLogicSystems/ALSProlog,AppliedLogicSystems/ALSProlog