First, I tested this code using the same deployment testing script I used on #5713 (submitting ver2 and ver3 blocks, with and without properly DER encoded signatures) over the p2p network to a node running the new code, and the switchover worked as expected.

I did notice that, unlike for the implementation in 0.10, we're not bumping the block version number here. I believe the only effect of that would be that mining nodes must upgrade to 0.10 or higher in order to implement the soft-fork, is that correct? I assume that is the intent?

@sdaftuar Eh, no, that was not the intent. Thanks for reviewing!

I've updated the code to produce v3 blocks, and also prevented non-DERSIG from entering the mempool (which should already be impossible due to standardness rules, but belt-and-suspenders...).

utACK