Small fix in BaseProblem.

extensions/base_problems/BaseProblem.h

@@ -94,7 +94,7 @@ public:
   }
 
   /// pointer to the feSpace of the problem
-  inline FiniteElemSpace* getFeSpace(int comp = 0) 
+  inline const FiniteElemSpace* getFeSpace(int comp = 0) 
   {
     return prob->getFeSpace(comp); 
   }