additional debugging and sanity for miner

Though I thought I had fixed the miner height bug, a user reported an error message that suggested the problem had not been fixed. It also appears like the problem may be more deep-seated than originally suggested, instead of being a problem with the miner module it might actually be a problem with the ConsensusChange propagation, which means that more modules than just the miner would be affected.

I've added more sanity checks and logging messages to the miner, we should be closer to getting to the bottom of this.