message: Remove fee from zerocoin spend
  fixes 596
diff: @@ -595,6 +595,7 @@ void CoinControlDialog::updateLabels(WalletModel *model, QDialog* dialog)
  std::vector<uint256> vCoinControlSerials;
  coinControl()->ListSelected(vCoinControlSerials);
  + bool fZerocoinMintSelected = false;
  for (auto serialHash: vCoinControlSerials) {
  CZerocoinMint mint;
  @@ -609,7 +610,7 @@ void CoinControlDialog::updateLabels(WalletModel *model, QDialog* dialog)
  }
  nQuantity++;
  -
  + fZerocoinMintSelected = true;
  nAmount += mint.GetDenominationAsAmount();
  }
  @@ -633,7 +634,12 @@ void CoinControlDialog::updateLabels(WalletModel *model, QDialog* dialog)
  nBytes -= 34;
  // Fee
  + if (fZerocoinMintSelected) {
  + nPayFee = 0; // No fee to spend zerocoin
  + }
  + else {
  nPayFee = model->wallet().getMinimumFee(nBytes, *coinControl(), nullptr /* returned_target */, nullptr /* reason */);
  + }
  if (nPayAmount > 0)
  {
  