CreateNewBlock() now takes scriptPubKey argument,
rather than a key.

CreateNewBlockWithKey() helper is added to restore existing functionality,
making this an equivalent-transformation change.
RPC: getblocktemplate does not require a key, to create a block template

getblocktemplate only uses certain portions of the coinbase transaction,
notably ignoring the coinbase TX output entirely.

Use CreateNewBlock() rather than CreateNewBlockWithKey(), eliminating
the needless key passing.

Should be zero behavior changes.
miner: constify CreateNewBlock() arg scriptPubKeyIn
Merge pull request #2928 from jgarzik/cnb-txout

CreateNewBlock / getblocktemplate cleaning