Two million byte size limit with sigop and sighash limits.

Proposed raising the maximum block size from 1 MB to 2 MB, with new limits on signature checks and hashing.

Bigger blocks could let an attacker build blocks that take a very long time to check. So alongside the 2 MB limit, it counted signature checks more accurately and capped the data hashed for signatures in each block. Older nodes would be cut off by the first block breaking the old limits.