message: Add coin stake check in transaction.
diff: @@ -376,7 +376,13 @@ public:
  bool IsCoinBase() const
  {
  - return (vin.size() == 1 && vin[0].prevout.IsNull());
  + return (vin.size() == 1 && vin[0].prevout.IsNull() && vout.size() >= 1);
  + }
  +
  + bool IsCoinStake() const
  + {
  + // ppcoin: the coin stake transaction is marked with the first output empty
  + return (vin.size() > 0 && (!vin[0].prevout.IsNull()) && vout.size() >= 2 && vout[0].IsEmpty());
  }
  friend bool operator==(const CTransaction& a, const CTransaction& b)
  