* mln/accu/center.hh: make it compute the mass center instead of the
	bbox center.

	* mln/core/site_set/p_graph_piter.hh: add element();

	* mln/debug/colorize.hh: Pass the color type as arguments instead of
	passing the return type as template parameter.

	* mln/debug/draw_graph.hh: add a new signature.

	* mln/literal/colors.hh,
	* mln/level/convert.hh: update comments.

	* mln/level/transform.spe.hh: add new specializations/dispatches when
	the function is of type Function_i2v.

	* mln/value/label.hh: Fix missing include.

git-svn-id: https://svn.lrde.epita.fr/svn/oln/trunk@2963 4aad255d-cdde-0310-9447-f3009e2ae8c0