[amg] add missing methods dot and norm to SequentialInformation

the two methods weren't needed up to now. After switching to dynamic
construction of the scalar product, they have to be defined, but still
they should not be called (currently). Thus we implement them with an
assert(false).

dune/istl/paamg/pinfo.hh

@@ -73,6 +73,18 @@ namespace Dune
         DUNE_UNUSED_PARAMETER(v);
       }
 
+      template<class T1, class T2>
+      void dot (const T1& x, const T1& y, T2& result) const
+      {
+        assert(false && "this function should never be called");
+      }
+
+      template<class T1>
+      typename FieldTraits<typename T1::field_type>::real_type norm (const T1& x) const
+      {
+        assert(false && "this function should never be called");
+      }
+
       template<class T>
       SequentialInformation(const CollectiveCommunication<T>&)
       {}