[cleanup] use true_type and false_type from std::

dune/common/dotproduct.hh

@@ -25,11 +25,11 @@ namespace Dune {
   struct AlwaysVoid { typedef void type; };
 
   template<class T, class = void>
-  struct IsVector : false_type {};
+  struct IsVector : std::false_type {};
 
   template<class T>
   struct IsVector<T, typename AlwaysVoid<typename T::field_type>::type>
-    : true_type {};
+    : std::true_type {};
 
   /** @brief computes the dot product for fundamental data types according to Petsc's VectDot function: dot(a,b) := std::conj(a)*b
    *