test_failing_import_sticks -- if an import raises an exception,
        ensure that trying to import it again continues raising exceptions
    test_failing_reload -- if a module loads OK, but a reload raises an
        exception, ensure that the module is still in sys.modules, and
        that its __dict__ reflects as much of the reload attempt as
        succeeded.  That doesn't seem like sane semantics, but it is
        backward-compatible semantics <wink>.