fixing a memory leak: the mapper_ member variable needs to be deleted in the destructor

[[Imported from SVN: r2013]]

fem/lagrangebase/lagrangespace.cc

@@ -52,6 +52,8 @@ namespace Dune {
     for(int i=0; i<numOfDiffBase_; i++)
       if (baseFuncSet_[i] != 0)
         delete baseFuncSet_[i];
+
+    delete(mapper_);
   }
 
   template< class FunctionSpaceT, class GridType, class IndexSetType , int polOrd, class DofManagerType >