Exposes an additional logger that uses the test's root logger as the
parent for any TestCase instances constructor by the hook. The fixture
logger still continues to be the parent of the hook logger.
Also changes the CleanEveryN hook to explicitly get marked as a failure
if a ServerFailure exception is thrown, rather than relying on
TestReport.combine() to do so implicitly.
Also defines a generic Registry metaclass for making class declarations
store a reference to the class along with a name so that they can be
looked up later.
