Rename empty in is_empty and add method pop_front, which
	return the front element and pop the queue.
	* mln/core/p_priority_queue.hh,
	* mln/core/p_priority_queue_fast.hh,
	* mln/core/p_queue.hh,
	* mln/core/p_queue_fast.hh: Update this modification.

	Update with these modifications.
	* mln/geom/seeds2tiling.hh,
	* mln/geom/seeds2tiling_with_chamfer.hh,
	* tests/core_p_priority_queue.cc,
	* tests/core_p_priority_queue_fast.cc: Update.

git-svn-id: https://svn.lrde.epita.fr/svn/oln/trunk@1470 4aad255d-cdde-0310-9447-f3009e2ae8c0