message: don't serialize nflags unless we have to
diff: @@ -39,7 +39,13 @@ public:
  SetNull();
  }
  - SERIALIZE_METHODS(CBlockHeader, obj) { READWRITE(obj.nVersion, obj.hashPrevBlock, obj.hashMerkleRoot, obj.nTime, obj.nBits, obj.nNonce, obj.nFlags); }
  + SERIALIZE_METHODS(CBlockHeader, obj)
  + {
  + READWRITE(obj.nVersion, obj.hashPrevBlock, obj.hashMerkleRoot, obj.nTime, obj.nBits, obj.nNonce);
  + // peercoin: do not serialize nFlags when computing hash
  + if (!(s.GetType() & SER_GETHASH) && s.GetType() & SER_POSMARKER)
  + READWRITE(obj.nFlags);
  + }
  void SetNull()
  {
  