Use VectorType::value_type::field_type instead of VectorType::field_type

BlockVectors should have both, but the former allows also std::vector<FieldVector>

[[Imported from SVN: r12353]]

dune/solvers/solvers/iterativesolver.hh

@@ -11,7 +11,7 @@
     template <class VectorType, class BitVectorType = Dune::BitSetVector<VectorType::block_type::dimension> >
     class IterativeSolver : public Solver
     {
-        typedef typename VectorType::field_type field_type;
+        typedef typename VectorType::value_type::field_type field_type;
 
         // For complex-valued data
         typedef typename Dune::FieldTraits<field_type>::real_type real_type;