Add support for executing tests in nested classes when parent class is targeted

[jcansdale]

E.g. allow the targeting of ParentClass:

    public class ParentClass
    {
        public class NestedClass
        {
            [Test]
            public void Pass()
            {
            }
        }
    }

[CharliePoole]

NUnit will eventually support this directly, but there's no schedule for it. See nunit/nunit#25

[jcansdale]

Thanks for the heads up. We just need to make sure that if a parent class and nested classes are targeted, it doesn't execute the nested classes twice (breaking the code I'm about to push). This probably won't be an issue, depending on how the test filters work.

[CharliePoole]

So long as you use a filter it shouldn't be a problem. Selecting something multiple times won't get it running twice.