[noise] MAC'ing recipient public key

[Trevor Perrin]

Another change:

The recipient pubkey is included in the additional authenticated data
for both box MACs.  This ensures that if the sender can decrypt a box,
it must have been encrypted to the sender's pubkey.  While this can
also be accomplished by taking care with the ECDH, I think it's
simpler to just include the recipient's key into the mac.

Also, I changed the order of arguments to ENCRYPT() to match
noise_body(), so authtext is always listed last.

https://github.com/trevp/noise/wiki/Boxes/_compare/02d72d5037ec2d83cb4342ea2b6f3a910d122412...51707f5223dbbeac09d64ec4c5a473b7be09ae34


Trevor