Enable Travis CI and Coveralls

See citusdata/cstore_fdw@b95f6d4, citusdata/cstore_fdw@0a988d6, and
citusdata/cstore_fdw@f3a56bb for more details. Will add badge once this
is confirmed working.
Make tests resilient to other ports

Missed some places that'll bite us with non-standard ports.
Fix SortList test wrapper

Turns out passing strcmp to qsort isn't possible. Added a wrapper.
Use 127.0.0.1 instead of localhost. in repair test

The latter _should_ resolve to localhost and was being used as an easy
synonym for it, but this hack isn't working in Travis. Switched to the
IP address instead, which I didn't think would work but does.