vertices.

	* mln/core/line_graph_psite.hh
	(mln::line_graph_psite<P>::first_id)
	(mln::line_graph_psite<P>::second_id):
	New methods.
	Use them to simplify...
	(mln::line_graph_psite<P>::first)
	(mln::line_graph_psite<P>::second): ...these ones.
	* mln/accu/count_adjacent_vertices.hh: New accumulator.
	* mln/morpho/closing_area_on_vertices.hh,
	* mln/morpho/opening_area_on_vertices.hh:
	New filters.
	* mln/morpho/closing_area.hh,
	* mln/morpho/opening_area.hh,
	* mln/morpho/closing_attribute.hh,
	* mln/morpho/opening_attribute.hh:
	Remove spurious comments.
	* tests/morpho/lena_line_graph_image_wst2.cc: Use
	morpho::closing_area_on_vertices instead of morpho::closing.


git-svn-id: https://svn.lrde.epita.fr/svn/oln/trunk@1802 4aad255d-cdde-0310-9447-f3009e2ae8c0