Add origin node to arc.

src/main/org/insa/graph/Node.java

@@ -30,7 +30,7 @@ public class Node implements Comparable<Node> {
 	 * 
 	 * @param arc Arc to the successor.
 	 */
-	public void addSuccessor(Arc arc) {
+	protected void addSuccessor(Arc arc) {
 		successors.add(arc);
 	}