title: MKMapView with multiple overlays memory-issue
body: <p>There seems to be an "issue" with overlays and the <code>MapKit</code>. Unlike annotations, overlays aren't reused and therefore when adding multiple overlays would cause memory-problems on a real device. I've had this problem multiple times. So my question is, how can I reuse the MKOverlay and so improve the performance of overlays on <code>MapKit</code>?</p>