message: Simplify Array2D assignment operator
diff: @@ -411,8 +411,7 @@ public:
  inline void operator=(const T &a)
  { array1d = a; }
  - inline Array2D& operator=(const Array2D &a)
  - { M = a.M; N = a.N; array1d = a.array1d; return *this; }
  + inline Array2D& operator=(const Array2D &a) = default;
  /// Make this Array a reference to 'master'
  inline void MakeRef(const Array2D &master)
  