message: [Consensus] Guard time checks changes
  Guard these changes against the protocol version change enforcement
diff: @@ -431,7 +431,7 @@ bool CheckProofOfStake(const CBlock block, uint256& hashProofOfStake, std::uniqu
  unsigned int nBlockFromTime = blockfrom.nTime;
  unsigned int nTxTime = block.nTime;
  - if (!txin.IsZerocoinSpend()) { //Equivalent for zPIV is checked above in ContextualCheckZerocoinStake()
  + if (!txin.IsZerocoinSpend() && nPreviousBlockHeight >= Params().Zerocoin_Block_Public_Spend_Enabled() - 1) { //Equivalent for zPIV is checked above in ContextualCheckZerocoinStake()
  if (nTxTime < nBlockFromTime) // Transaction timestamp nTxTime
  return error("CheckStakeKernelHash() : nTime violation - nBlockFromTime=%d nTimeTx=%d", nBlockFromTime, nTxTime);
  if (nBlockFromTime + nStakeMinAge > nTxTime) // Min age requirement
  