Implement functions in SequentialInformation

Summary

Implement dot() and norm() in Amg::SequentialInformation to have it closer to a sequential analog of parallel information like OwnerOverlapCopyCommunication.

Discussion

Why should dot and norm not be called in a sequential setup? Maybe this SequentialInformation is mostly used for tagging functions. If so, then a shorter tag::sequential would be cleaner. If the interface is required but is not allowed to be used in a sequential setup then this is a design flaw. But, maybe I just don't understand the usage of this class. In a generic setting it would be nice to have a sequential analog to the parallel communicators, though.

dune/istl/paamg/pinfo.hh

@@ -69,17 +69,15 @@ namespace Dune
       {}
 
       template<class T1, class T2>
-      void dot (const T1&, const T1&, T2&) const
+      void dot (const T1& x, const T1& y, T2& result) const
       {
-        // This function should never be called
-        std::abort();
+        result = x.dot(y);
       }
 
       template<class T1>
-      typename FieldTraits<typename T1::field_type>::real_type norm (const T1&) const
+      typename FieldTraits<typename T1::field_type>::real_type norm (const T1& x) const
       {
-        // This function should never be called
-        std::abort();
+        return x.two_norm();
       }
 
       template<class T>