message: rpc: make sure `gettxoutsetinfo` hash has txids
  The key (transaction id for the following outputs) should be serialized
  to the HashWriter.
  This is a problem as it means different transactions in the same
  position with the same outputs will potentially result in the same hash.
  Fixes primary concern of
diff: @@ -133,6 +133,7 @@ bool CCoinsViewDB::GetStats(CCoinsStats &stats) const {
  if (pcursor->GetKey(key) && key.first == DB_COINS) {
  if (pcursor->GetValue(coins)) {
  stats.nTransactions++;
  + ss << key;
  for (unsigned int i=0; i<coins.vout.size(); i++) {
  const CTxOut &out = coins.vout[i];
  if (!out.IsNull()) {
  