Downside: we copy points at each comparison, which is terrible! No noticeable
changes when profiling the construction of a triangulation.
We need this copy because of Lazy kernel: despite construct_point_3 having
const Point_3& construct_point_3_object()(const Point_3&)
the Lazy kernel can return some copies.
Other solutions that were not used:
-- Distinguish the Ouput type of Unary_function_to_property map depending on
the type of Kernel (ugly and not safe)
-- Use Weighted_point_mappers traits (but that blood will not be on my hands)
Mael Rouxel-Labbé
2a06660a2b