* Add PruningPointProof to externalapi.
* Add BuildPruningPointProof and ValidatePruningPointProof to Consensus.
* Add the pruning point proof to the protocol.
* Add the pruning point proof to the wire package.
* Add PruningPointBlueWork.
* Make go vet happy.
* Properly initialize PruningPointProof in consensus.go.
* Validate pruning point blue work.
* Populate PruningPointBlueWork with the actual blue work of the pruning point.
* Revert "Populate PruningPointBlueWork with the actual blue work of the pruning point."
This reverts commit f2a9829998.
* Revert "Validate pruning point blue work."
This reverts commit c6a90c5d2c.
* Revert "Properly initialize PruningPointProof in consensus.go."
This reverts commit 9391574bbf.
* Revert "Add PruningPointBlueWork."
This reverts commit 48182f652a.
* Fix PruningPointProof and MsgPruningPointProof to be two-dimensional.
* Fix wire PruningPointProof to be two-dimensional.
