Adds GenericXUnitTestEngine unit test engine to handle any test script that
produces XUnit test results.
Any changes in this vein need to wait for T5568 and be reframed on top of that.
Although I think the idea in T5568 is great it looks a bit stale and having .arcunit looks a bit harder than having .arclint due to its complexities. I think this test engine solves a real problem and may actually help you reduce unit test related issues (since I have no access to your support data, I am completely making this up :D)