Bug: zone_list being added to wrong tile configuration

[shred86]

If you're specifying custom zoom levels for multiple tiles then batch building, all within the same “session”, it appears zone_list is just being appended with all of the zones you specified in every tile and being written to each tile configuration. In other words, each tile configuration ends up having zones that aren't even within its geographic region.

It doesn’t appear to have an affect on the output for each tile but still doesn’t seem like desired behavior.

Fixed in #269