Threaded test cases

Having a test case that spans multiple threads to check for thread-safety or interaction is a fairly common task. This puts the following requirements over the framework:
thread-safety
ability for the framework to merge failures occurring in created thread with failures of the originating test case.

Merging failures of created thread with the original thread failures

Assertions that occur in threads spawned by a test case need to be transfered to the main test framework thread and associated with the test case. The framework should provides a functor decorated that ensure that when the decorated functor is executed in the created thread, it associates failures with the original test failures.