Test command takes files

This handles #996. Some additional points:

* This pull currently depends on a private bultitude fn, `read-ns-form`. Ideally, the fn that uses it, `ns-form-for-file`, should live in bultitude, I don't know what process we want for this. I can open a pull for bultitude but then I don't know how long we'll be waiting before we can depend on a new release.
*  I also added more tests for `lein test` and made `abort-msg` a test helper fn.
* I removed a failing test that was introduced by dfb951f430eb360d7f17128258968289d160381e