Update display when a test case is done

Property definitions

nitc $ NitUnitExecutor :: mark_done
	# Update display when a test case is done
	fun mark_done(du: DocUnit)
	do
		du.is_done = true
		toolcontext.clear_progress_bar
		toolcontext.show_unit(du)
		show_status
	end
src/testing/testing_doc.nit:86,2--93,4