upgrade leaflet to 0.6.4

Source https://github.com/Leaflet/Leaflet/archive/v0.6.4.zip

Compressed files based by:
* http://cdn.leafletjs.com/leaflet-0.6.4/leaflet.css
* http://cdn.leafletjs.com/leaflet-0.6.4/leaflet.ie.css
* http://cdn.leafletjs.com/leaflet-0.6.4/leaflet.js

Images compressed with optipng.