message: Change GetProofOfStake to use header prevout info instead of transaction data
diff: @@ -162,7 +162,7 @@ public:
  std::pair<COutPoint, unsigned int> GetProofOfStake() const //qtum
  {
  - return IsProofOfStake()? std::make_pair(vtx[1]->vin[0].prevout, nTime) : std::make_pair(COutPoint(), (unsigned int)0);
  + return IsProofOfStake()? std::make_pair(prevoutStake, nTime) : std::make_pair(COutPoint(), (unsigned int)0);
  }
  CBlockHeader GetBlockHeader() const
  