Defines for_each_sample algorithm.

namespace boost {
  namespace unit_test {
    namespace data {
      template<typename Action, typename T> 
        void invoke_action(Action const & action, T const & arg);
      template<typename Action, typename... T, std::size_t... I> 
        void invoke_action_impl(Action const & action, 
                                std::tuple< T const &...> const & args, 
                                index_sequence< I...> const &);
      template<typename Action, typename... T> 
        void invoke_action(Action const & action, 
                           std::tuple< T const &...> const & args);
      template<typename DataSet, typename Action> 
        std::enable_if< monomorphic::is_dataset< DataSet >::value, void >::type 
        for_each_sample(DataSet const & samples, Action const & act, 
                        data::size_t number_of_samples = BOOST_TEST_DS_INFINITE_SIZE);
    }
  }
}