only use tiles from max 3 zoom-levels above current
only use tiles from max 3 zoom-levels above current

- this only cancels open requests that don't add much to the current view

cleeus/tangram-es,cleeus/tangram-es,cleeus/tangram-es,tangrams/tangram-es,tangrams/tangram-es,quitejonny/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,cleeus/tangram-es,tangrams/tangram-es,quitejonny/tangram-es,quitejonny/tangram-es,cleeus/tangram-es,cleeus/tangram-es,tangrams/tangram-es,tangrams/tangram-es,quitejonny/tangram-es,tangrams/tangram-es,quitejonny/tangram-es