Rewrite CI scripts

This PR removes the need for a `Makefile` for the purposes of CI. We
take advantage of Travis CI now considering the `ghc:` section of
`.travis.yml` as an extra dimension in the build matrix, so that we
don't need to use @hvr's multi-ghc ppa anymore.

Travis CI is made to build on whatever point release of GHC 7.4, GHC 7.6
and GHC 7.8 they currently have installed. Build currently fails on GHC
7.4 pending the merge of an [8 months one-liner PR](https://github.com/haskell-distributed/distributed-process-tests/pull/1).

Further, whereas before, CI only tested whether distributed-process
builds, now CI runs the tests from the distributed-process-tests package
to check that everything is ok.