Gets travis cross platform testing working. Based on the templates from: japaric/trust/commit/29b0e084ff2c40d1aa1b6a5d66ab81eca90439e1
* Run integration tests on multiple shells To make sure that I don't break tests for shells other than my dev-box's `sh` and the `sh` on travis, each integration test case now runs using `sh`, `dash`, and `bash.