FIT KV: New Subdoc errors

These tests:

• Subdocument get for a document that contains too many levels to parse, should error with Path/DocumentTooDeepException
• Subdocument insert for a document that contains too many levels to parse, should error with PathTooDeepException
• Inserting some content that will make the document too deep, should error with ValueTooDeepException
• mutateInReallyLongPath()

Are failing with various errors.