Method convert

java/Chapter 17/Question17_13/QuestionC.java:77–82

(BiNode root)

	}
	
	public static BiNode convert(BiNode root) {
		BiNode head = convertToCircular(root);
		head.node1.node2 = null;
		head.node1 = null;
		return head;
	}
	
	public static void concat(BiNode x, BiNode y) {
		x.node2 = y;