* mln/topo/is_simple_point3d.hh
	(mln::topo::is_simple_point3d<I, N>::init_): New method.
	(connectivity_number_fun_t): New (private) typedef.
	(connectivity_number_fg, connectivity_number_bg):
	New (private) members.
	Initialize them...
	(mln::topo::is_simple_point3d<I, N>::is_simple_point3d):
	...from the ctors, using init_().