[Tile-serving] [osm2pgsql] Fix warnings when compiling tests, use -Werror with travis (#395)

[Paul Norman]

I turned off `-Werror` with g++ and reported warnings from osmium in osmcode/libosmium#99.

I think this is ready for review now.

---
Reply to this email directly or view it on GitHub:
https://github.com/openstreetmap/osm2pgsql/pull/395#issuecomment-121844400
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/tile-serving/attachments/20150715/10134558/attachment.html>