Great Consensus Cleanup Revival

[MattCorallo]

@ajtowns

The idea isn’t to encode the height in the coinbase witness, just to require that the coinbase have some witness. That ensures there’s an OP_RETURN output in every future coinbase that isn’t present in any of the potentially duplicatable existing coinbases.

Ah, fair enough. I’d still very much love to see the nLockTime set to the block height, it makes pulling the block height out of the coinbase transaction simpler, though its not a super critical difference.