* mln/convert/to_image.hh: Fix.
	* mln/linear/line_convolve.hh: Add todo.
	* mln/canvas/labeling.hh: Add comments.
	* mln/labeling/flat_zones.hh,
	* mln/labeling/foreground.hh,
	* mln/labeling/regional_minima.hh,
	* mln/labeling/regional_maxima.hh: Add precondition.
	* mln/labeling/background.hh: .
	* mln/labeling/level.hh (level_): Rename as...
	(level_t): ...this.
	(level_): New.


git-svn-id: https://svn.lrde.epita.fr/svn/oln/trunk@1075 4aad255d-cdde-0310-9447-f3009e2ae8c0