* mln/core/concept/value_set.hh
	(operator<<(std::ostream&, const Value_Set<E>&))
	* mln/morpho/tree/data.hh
	(operator<< (std::ostream&, const tree::data<I, S>&)):
	Use the stream passed as argument instead of std::cout.
	* mln/util/fibonacci_heap.hh
	(mln::util::internal::fibonacci_heap_node::print_): Take an output
	stream as argument instead of using the standard output.
	(mln::util::fibonacci_heap::print_): Rename first argument from
	`cout' to `ostr' prevent confusions with std::cout.
	* mln/trace/warning.hh (mln::trace::warning): Print warnings on
	the standard error instead of the standard ourput.