message: reconsider prevout for sigma
diff: @@ -1177,7 +1177,7 @@ bool CheckTransaction(
  return state.DoS(100, false, REJECT_INVALID, "bad-cb-length");
  } else {
  BOOST_FOREACH(const CTxIn &txin, tx.vin) {
  - if (txin.prevout.IsNull() && !txin.scriptSig.IsZerocoinSpend() && !txin.scriptSig.IsZerocoinSpendV3()) {
  + if (txin.prevout.IsNull() && !txin.scriptSig.IsZerocoinSpend()) {
  return state.DoS(10, false, REJECT_INVALID, "bad-txns-prevout-null");
  }
  }
  