message: Improve the performance of xthin queue jumping
  Use an std::swap rather than a copy operation to push xthin messages
  to the front of the queue.
diff: @@ -591,8 +591,10 @@ bool CNode::ReceiveMsgBytes(const char *pch, unsigned int nBytes)
  strCommand == NetMsgType::XTHINBLOCK || strCommand == NetMsgType::THINBLOCK ||
  strCommand == NetMsgType::XBLOCKTX || strCommand == NetMsgType::GET_XBLOCKTX)
  {
  - vRecvMsg.push_front(msg);
  + vRecvMsg.push_front(CNetMessage(GetMagic(Params()), SER_NETWORK, nRecvVersion));
  + std::swap(vRecvMsg.front(), vRecvMsg.back());
  vRecvMsg.pop_back();
  +
  LogPrint("thin", "Receive Queue: pushed %s to the front of the queue\n", strCommand);
  }
  }
  