[Tile-serving] [osm2pgsql] update libosmium to release version 2.5.0 (#495)

[Paul Norman]

Builds and looks okay on my system, so it's okay to merge, but I'm holding off in case we want to go right to 2.5.1

---
Reply to this email directly or view it on GitHub:
https://github.com/openstreetmap/osm2pgsql/pull/495#issuecomment-154040050
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openstreetmap.org/pipermail/tile-serving/attachments/20151105/105bdc99/attachment-0001.html>