Configure Travis CI for GEOS (#657)

Configurations for GCC and clang with both Autotools and CMake.
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Contributed by Mateusz Loskot <mateusz@loskot.net>

git-svn-id: http://svn.osgeo.org/geos/branches/3.4@3915 5242fede-7e19-0410-aef8-94bd7d2200fb