Add scripted test for https://github.com/sbt/junit-interface/issues/14

The test included in this pull request reproduces the behaviour seen in https://github.com/sbt/junit-interface/issues/14.

I've taken a look at the patch submitted by szeiger and I've found the cause of the issue - it ignores suite runners based on class names rather than examining the type of the suite runner. If you use @RunWith with a subclass of Suite, your tests will still be run twice. To reproduce the problem, I simply subclassed Suite and annotated MyTest to @RunWith the new runner.