Still broken, but a lot of retarded fixed.

Crypto had the wrong idea entirely of slot size, and didn't know nacl
prepends the nonce (and then refuses to decrypt without manually
splitting it back up). A good few hours poring over hex. Can't mutate
a wrapped object either, because I don't want to make a __setattribute__
that catches and updates wrapper attributes, so self.levels = [] = BAD
s/KEY/CHK/ because 'content hash key' is less easy to confuse with
encryption keys.