message: Make VectorConstantCoefficient::GetVec const (const-correctness)
diff: @@ -491,7 +491,7 @@ public:
  const IntegrationPoint &ip) { V = vec; }
  /// Return a reference to the constant vector in this class.
  - const Vector& GetVec() { return vec; }
  + const Vector& GetVec() const { return vec; }
  };
  /** @brief A piecewise vector-valued coefficient with the pieces keyed off the
  