message: Use const in COutPoint class
diff: @@ -21,7 +21,9 @@ public:
  uint256 hash;
  uint32_t n;
  - COutPoint(): n((uint32_t) -1) { }
  + static constexpr uint32_t NULL_INDEX = std::numeric_limits<uint32_t>::max();
  +
  + COutPoint(): n(NULL_INDEX) { }
  COutPoint(const uint256& hashIn, uint32_t nIn): hash(hashIn), n(nIn) { }
  ADD_SERIALIZE_METHODS;
  @@ -32,8 +34,8 @@ public:
  READWRITE(n);
  }
  - void SetNull() { hash.SetNull(); n = (uint32_t) -1; }
  - bool IsNull() const { return (hash.IsNull() && n == (uint32_t) -1); }
  + void SetNull() { hash.SetNull(); n = NULL_INDEX; }
  + bool IsNull() const { return (hash.IsNull() && n == NULL_INDEX); }
  friend bool operator<(const COutPoint& a, const COutPoint& b)
  {
  