banUnknownProperties may not correctly handle the anyOf keyword

[pbatey]

Based on the discussion about banUnknownProperties not being supported by ajv and the fact that one of the reasons they don't support it is because of the anyOf keyword...

banUnknownProperties is not likely handling keywords like anyOf correctly. It adds additionalProperties: false to anyOf children -- not sure what it would do -- I haven't run into a use-case where I needed to use anyOf.

BTW: banUnknownProperties isn't doing anything with the not keyword -- which I think is correct, at least for my use-case where I want to check for misspellings in a JSON object.