[Tile-serving] [osm2pgsql] Change z_order of link roads and add tests (#374)

[math1985]

> z_order is included for railways

Sorry, I meant the value added to the z_order, as in this PR. It would be nice if a naive rendering of all roads+railways ordered by z_order would result in railways rendered on top of roads - currently, railways would be rendered below roads.

---
Reply to this email directly or view it on GitHub:
https://github.com/openstreetmap/osm2pgsql/pull/374#issuecomment-119543590
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/tile-serving/attachments/20150708/5908929e/attachment.html>