* headers.mk: add new headers to distribution.

	* mln/util/soft_heap.hh: new file. New implementation. New members may
	be added later.

	* mln/util/tracked_ptr.hh: Fix an issue while assigning a null
	tracked_ptr to another tracked_ptr. An internal pointer was not
	initialized but dereferenced and led to a segfault.

	* tests/unit_test/Makefile.am,
	* tests/unit_test/mln_util_soft_heap.cc: add a new unit test.

	* tests/util/Makefile.am,
	* tests/util/soft_heap.cc: add a new test.

git-svn-id: https://svn.lrde.epita.fr/svn/oln/trunk@3161 4aad255d-cdde-0310-9447-f3009e2ae8c0