protocol_tx in submitted blocks. P2pool previously hardcoded an empty
protocol_tx (0 outputs), causing block rejections with "Invalid number
of outputs in protocol_tx".
Now fetches the daemon's blocktemplate_blob via getblocktemplate RPC,
parses out the real protocol_tx bytes, and uses them in the block
template. Falls back to the empty protocol_tx when the RPC hasn't
returned yet (correct for blocks with no payouts due).
Matt Hess