Add image point iterators parameterized by the image topology;
	factor code into an internal class.
	
	* oln/core/gen/bbox_fwd_piter.hh: Change inheritance and move
	methods into...
	* oln/core/internal/bbox_fwd_piter.hh: ...this new class.
	* oln/core/gen/bbox_bkd_piter.hh: Change inheritance and move
	methods into...
	* oln/core/internal/bbox_bkd_piter.hh: ...this new class.
	* oln/core/gen/fwd_piter_bbox.hh: New.
	* oln/core/gen/bkd_piter_bbox.hh: New.



git-svn-id: https://svn.lrde.epita.fr/svn/oln/trunk@556 4aad255d-cdde-0310-9447-f3009e2ae8c0