Fixed bug: we default aerialway to the blank string, so it will always be `not None`. Further, testing `in` a single tuple doesn't make much sense, and that isn't how it's spelled anyway (should be `in ('chair_lift',)`.
Fixed bug: we default aerialway to the blank string, so it will always be `not None`. Further, testing `in` a single tuple doesn't make much sense, and that isn't how it's spelled anyway (should be `in ('chair_lift',)`.

mapzen/TileStache,mapzen/TileStache,mapzen/TileStache