Defines range generator.

namespace boost {
  namespace unit_test {
    namespace data {
      template<typename SampleType, typename Params> 
        monomorphic::generated_by< monomorphic::xrange_t< SampleType > > 
        xrange(Params const &);
      template<typename SampleType> 
        monomorphic::generated_by< monomorphic::xrange_t< SampleType > > 
        xrange(SampleType const & end_val);
      template<typename SampleType, typename Params> 
        enable_if_c< nfp::is_named_param_pack< Params >::value, monomorphic::generated_by< monomorphic::xrange_t< SampleType > > >::type 
        xrange(SampleType const & end_val, Params const & params);
      template<typename SampleType> 
        monomorphic::generated_by< monomorphic::xrange_t< SampleType > > 
        xrange(SampleType const & begin_val, SampleType const & end_val);
      template<typename SampleType, typename StepType> 
        monomorphic::generated_by< monomorphic::xrange_t< SampleType > > 
        xrange(SampleType const & begin_val, SampleType const & end_val, 
               StepType const & step_val);
      namespace monomorphic {
        template<typename SampleType, typename StepType = SampleType> 
          class xrange_t;
      }
    }
  }
}