Update Layer.Raphael.js

Added a new div under overlayPane for raphaelRoot.  This allows raphael objects to "play nicely" with other non-Raphael SVG and VML objects that are also plotted on the map at the same time.  

Without this extra div, non-Raphael objects have some erratic behavior:  they sometimes disappear and/or are offset incorrectly, especially after panning and zooming.