Nef_3: SNC_structure cleanup - easier debugging

[GilesBathgate]

Summary of Changes

In SNC_structure there is a pattern for creating 'nodes'

vertices_.push_back(* get_vertex_node(Vertex()));

This is confusing when compiled in debug mode because without optimisations the Vertex() gets initialised in the callee but it's just used as a 'tag' parameter, and the allocator in the get_vertex_node function creates the real instance. All of the get_x_node functions essentially do the same thing using a different allocator, so they can be simplified to a single template function. The same can be done for the put_x_node functions. Replacing these reduces the amount of 'boilerplate' code.

Release Management

• Affected package(s): Nef_3
• Issue(s) solved (if any): cleaning / easier debugging
• License and copyright ownership: Returned to CGAL authors