message: make GetOsc at const member function
diff: @@ -393,7 +393,7 @@ public:
  void SetIntRule(const IntegrationRule *irs_[]) { irs = irs_; }
  // Return the value of the global relative data oscillation
  - double GetOsc() { return global_osc; }
  + const double GetOsc() { return global_osc; }
  // Return the local relative data oscillation errors
  Vector GetLocalOscs()
  