onMouseOver = function (e) {
				var target = e.target,
					point;

				if (chart.hoverSeries !== series) {
					series.onMouseOver();
				}
				while (target && !point) {
					point = target.point;
					target = target.parentNode;
				}
				if (point !== UNDEFINED && point !== chart.hoverPoint) { // undefined on graph in scatterchart
					point.onMouseOver(e);
				}
			}
Add tracking event listener to the series group, so the point graphics
themselves act as trackers