The function object Hilbert_sort_2<Traits, PolicyTag> sorts iterator ranges of
Traits::Point_2 along a Hilbert curve by recursively subdividing
at the median
or the middle depending on the PolicyTag.
Requirements
Traits is a model for SpatialSortingTraits.
Creation
Hilbert_sort_2<Traits, PolicyTag> o ( const Traits &traits = Traits());
constructs an instance with traits as traits class instance.