Activation code for a two megabyte block size increase.
Activation condition:
750 of 1000 blocks with version bit 0x10000000 set, then a four-week
(28-day) grace period, after which miners may create 2MB
blocks.
Conflicts:
qa/pull-tester/rpc-tests.sh
qa/rpc-tests/bipdersig-p2p.py
src/chainparams.cpp
src/main.cpp
src/miner.cpp
Additionall; Fix unit test.
Instead of relying on default, specify block size.
