* mln/morpho/attribute/volume.hh: New.
	* mln/morpho/closing_algebraic.hh: Copy to...
	* mln/morpho/opening_algebraic.hh: ...this new file.
	Make it a closing.
	* mln/canvas/morpho/algebraic_filter.hh (todo): New.
	* tests/morpho/closing_volume.cc: Test that the new version
	with morpho::attribute::volume gives the same result as the
	former version.


git-svn-id: https://svn.lrde.epita.fr/svn/oln/trunk@3344 4aad255d-cdde-0310-9447-f3009e2ae8c0