* mln/morpho/reconstruction/by_dilation/union_find.hh,
	* mln/morpho/reconstruction/by_erosion/union_find.hh
	(union_find_dispatch(image::kind::logic, Image, Image, Neighborhood)):
	Here.
	* tests/morpho/reconstruction/by_dilation/union_find.cc,
	* tests/morpho/reconstruction/by_erosion/union_find.cc:
	Rename as...
	* tests/morpho/reconstruction/by_dilation/union_find_on_functions.cc,
	* tests/morpho/reconstruction/by_erosion/union_find_on_functions.cc:
	...these.
	* tests/morpho/reconstruction/by_dilation/union_find_on_sets.cc,
	* tests/morpho/reconstruction/by_erosion/union_find_on_sets.cc:
	New tests.
	* tests/morpho/reconstruction/by_dilation/Makefile.am,
	* tests/morpho/reconstruction/by_erosion/Makefile.am:
	Adjust.
	(check_PROGRAMS): Add union_find_on_sets.
	(union_find_on_sets_SOURCES): New.
	(XFAIL_TESTS): New.  Add union_find_on_sets.