* mln/level/approx/median.hh: call diameter() instead of length() on
	win::ball.

	* mln/level/convert.hh: fix a return type.

	* mln/morpho/closing/essential.hh,
	* mln/morpho/essential.hh,
	* mln/morpho/opening/essential.hh: Fix includes.

git-svn-id: https://svn.lrde.epita.fr/svn/oln/trunk@3470 4aad255d-cdde-0310-9447-f3009e2ae8c0