Use tiled=true for superoverlays

Andrea did some nice improvements to do metaTiling, which leads to better performance and better labeling. We should leverage this infrastructure for KML superoverlays as well. Indeed when JTileCache comes it will likely be plugged in to this infrastructure. So we should make use of it, though we'll have to ask him how to do so, you turn tiled=true on, but you also have to do something with the origin. Though I feel like there should be some easier way for this case, since it's only 4326 and it's the world.