Also add a test to check case when 3rd arg is 0.

And then it can run with the native emitter.

Improves coverage because it tests the case where the arg does not have a
__len__ slot.

There is now just the exception instance on the stack when an exception is
raised, not the full (type, exc, traceback).

These additional special methods are enabled on most ports so we can test
them in this test.

See issue #2264.