log tileunload and moveend (update) events
abort request on tileunload

Fixes duplicate loading of tiles when panning fast back and forth (best
observable with county tiles at zoom 7). This happend when tiles were
already unloaded again (option unloadInvisibleTiles = true) while the
request was still pending.
extract TileQueue
Web Workers with Communist
update binary
add TileQueue
Leaflet.label patch as separate, reusable file
patch conditional + export
map + tile zoom in debug output (adjustTilePoint)
tile loading progress layer
extract overzoom
quick fix for serverZooms undefined
Leaflet 0.6
Merge branch 'dev' into gh-pages