message: Pass a hash reference to mempool.exists() rather than the hash
diff: @@ -624,12 +624,12 @@ public:
  return totalTxSize;
  }
  - bool exists(uint256 hash) const
  + bool exists(const uint256 &hash) const
  {
  READLOCK(cs);
  return (mapTx.count(hash) != 0);
  }
  - bool _exists(uint256 hash) const { return (mapTx.count(hash) != 0); }
  + bool _exists(const uint256 &hash) const { return (mapTx.count(hash) != 0); }
  double TransactionsPerSecond()
  {
  boost::mutex::scoped_lock lock(cs_txPerSec);
  