Set up Travis CI

Broke up the monolithic shell script into separate steps so the output
is clearer when it fails. These scripts are just thrown into a gist for
now at https://gist.github.com/jasonmp85/9963879. I had to enhance them
to allow a `PG_PRELOAD` environment variable to inform Travis what libs
should be preloaded (i.e. if the extension being tested has hooks).