1/ The requirement on the constructor of
Polyhedral_mesh_domain_with_features_3 was wrong: the argument must be
convertible to Mesh_polyhedron_3, and not to Polyhedron_3.
2/ The geom traits of Mesh_polyhedron_3<Gt> must be model of
PolyhedronTraits_3 *and* of IntersectionGeometricTraits_3.
(That patch passes the manual testsuite.)
