* mln/topo/center_only_iter.hh,
	* mln/topo/face.hh,
	* mln/trait/images.hh,
	* mln/convert/from_to.hxx,
	* mln/core/image/dmorph/sub_image.hh,
	* mln/core/routine/init.hxx,
	* mln/algebra/vec.hh: Make declaration and forward declarations
	consistent.

	* mln/canvas/browsing/backdiagonal2d.hh,
	* mln/canvas/browsing/breadth_first_search.hh,
	* mln/canvas/browsing/depth_first_search.hh,
	* mln/canvas/browsing/diagonal2d.hh,
	* mln/canvas/browsing/directional.hh,
	* mln/canvas/browsing/fwd.hh,
	* mln/canvas/browsing/hyper_directional.hh,
	* mln/canvas/browsing/snake_fwd.hh,
	* mln/canvas/browsing/snake_generic.hh,
	* mln/canvas/browsing/snake_vert.hh,
	* mln/fun/v2v/hsl_to_rgb.hh,
	* mln/literal/black.hh,
	* mln/literal/colors.hh,
	* mln/literal/white.hh: Add a default constructor for global
	variable types.

	* mln/canvas/browsing/internal/graph_first_search.hh: Avoid a
	warning for an unused variable.

	* mln/data/was.median.hh: Fix type of the reference.