message: Add comments to describe why we need to check inputs for Sigma spend
diff: @@ -3429,6 +3429,8 @@ void CWallet::CommitTransaction(CWalletTx& tx)
  bool zeroSpend = tx.IsZerocoinSpend() || tx.IsZerocoinSpendV3();
  CValidationState state;
  + // The old Zerocoin spend use a special way to check inputs but not for Sigma spend.
  + // The Sigma spend will share the same logic as normal transactions for inputs checking.
  if (!tx.AcceptToMemoryPool(false, maxTxFee, state, !tx.IsZerocoinSpend(), zeroSpend)) {
  LogPrintf("CommitTransaction(): Transaction cannot be broadcast immediately, %s\n", state.GetRejectReason());
  // TODO: if we expect the failure to be long term or permanent, instead delete wtx from the wallet and return failure.
  @@ -5618,7 +5620,9 @@ bool CWallet::CommitZerocoinSpendTransaction(CWalletTx &wtxNew, CReserveKey &res
  if (fBroadcastTransactions) {
  CValidationState state;
  - // Broadcast
  +
  + // The old Zerocoin spend use a special way to check inputs but not for Sigma spend.
  + // The Sigma spend will share the same logic as normal transactions for inputs checking.
  if (!wtxNew.AcceptToMemoryPool(false, maxTxFee, state, wtxNew.IsZerocoinSpendV3(), true)) {
  LogPrintf("CommitZerocoinSpendTransaction(): Transaction cannot be broadcast immediately, %s\n",
  state.GetRejectReason());
  