For the moment, the manifold feature is no longer working.
Merge remote-tracking branch 'cgal-dev/Mesh_3-manifold_criterion-lrineau' into Mesh_3-manifold_criterion-lrineau
Conflicts:
Mesh_3/include/CGAL/Mesh_3/Mesh_complex_3_in_triangulation_3_base.h
Mesh_3/include/CGAL/Mesh_3/Mesher_3.h
Mesh_3/include/CGAL/Mesh_3/Refine_facets_3.h
Polyhedron/demo/Polyhedron/Polyhedron_3.cpp
Polyhedron/demo/Polyhedron/Polyhedron_demo_mesh_3_plugin.cpp
Polyhedron/demo/Polyhedron/Polyhedron_demo_mesh_3_plugin_cgal_code.cpp