Some specifics on consensus changes:
* Transactions must be anchored to a real anchor in the chain.
* Anchors are pushed and popped during ConnectBlock/DisconnectBlock as appropriate.
* DisconnectTip triggers evictions, under some circumstances, of transactions in the
mempool which are anchored to roots that are no longer valid.
* Commitments append to the tree at the current best root during ConnectBlock.
* PourTxs cannot appear in coinbase transactions.
* Transactions can only contain empty vin/vouts if they contain a PourTx.
* PourTx public values must be well-formed (not negative or too large).
* Transactions cannot have the same serial twice throughout all PourTxs.
Transactions of version 2 and above contain a `vpour` field which is a vector of `CPourTx`
objects that embody our protocol. We introduce serialization primitives for boost::array
(we intend for changing the amount of inputs and outputs in the circuit to be simple).
SIGHASH_* operations hash this field like any other for now.
Sean Bowe