constness of some functions added

AMDiS/src/ProblemStat.h

@@ -280,12 +280,22 @@ namespace AMDiS {
     {
       return solution;
     }
+    
+    inline SystemVector const* getSolution() const
+    {
+      return solution;
+    }
 
     inline DOFVector<double>* getSolution(int i)
     {
       return solution->getDOFVector(i);
     }
 
+    inline DOFVector<double> const* getSolution(int i) const
+    {
+      return solution->getDOFVector(i);
+    }
+
     /// Returns \ref rhs.
     inline SystemVector* getRhs()
     {