Include accuracy property in 'locationfound' events.

I am submitting a patch adding back the `accuracy` property to `locationfound` events originating from `Map.Geolocation`. I believe it is desirable that a plugin bolstering Leaflet's geolocation wrapper, such as the otherwise currently broken [domoritz/leaflet-locatecontrol](https://github.com/domoritz/leaflet-locatecontrol), would have access to this property in some way.