Issue 188

This pull request resolves two critical problems with regard to test execution:

1. Fixtures, suites or even assemblies with no tests contained or with all tests removed through filtering cause the test worker thread to hang and the run never terminates.

2. Fixtures, suites and assemblies with no tests are running OneTimeSetUp and OneTimeTearDown, which wastes resources and can even lead to errors reported in fixtures not selected to run.

Fixes #188