[pdal] PostGIS for Travis CI configuration

[Mateusz Loskot]

Folks,

I added basic setup of Travis CI service for PDAL.
The status page is available here

https://travis-ci.org/PDAL/PDAL

In next iterations, I'm going to configure build with all features,
so all tests are run.

Travis CI uses Ubuntu 12.04, so it installs some newer packages
from ppa:ubuntugis, like GDAL 1.9.
I have question about PostgreSQL/PostGIS, what versions we
need in order to build with -DWITH_PGPOINTCLOUD=ON?

Are we fine with stable
ppa:ubuntugis/ppa
or
ppa:ubuntugis/ubuntugis-unstable
or
do we need to build PostGIS?

Best regards,
-- 
Mateusz  Loskot, http://mateusz.loskot.net