Better handling of unexpected topic exceptions for pyvows

currentoutput

============
 Vows Results
 ============

    A
      B

       Error in topic:
      integer division or modulo by zero
      
Traceback (most recent call last):
        File "/python/site-packages/pyvows/runner/gevent.py", line 104, in _run_setup_and_topic
    topic = topic_func(*topic_list)
        File "/testerror.py", line 13, in topic
    return 42 / 0
ZeroDivisionError: integer division or modulo by zero

      Nested tests following this error have not been run.
  ✓ OK » 0 honored • 0 broken (0.000301s)

expectedoutput

teardown

 ============
 Vows Results
 ============


    A
      B

       Error in topic:
      integer division or modulo by zero
      
Traceback (most recent call last):
        File "/python/site-packages/pyvows/runner/gevent.py", line 104, in _run_setup_and_topic
    topic = topic_func(*topic_list)
        File "/testerror.py", line 13, in topic
    return 42 / 0
ZeroDivisionError: integer division or modulo by zero

      Nested tests following this error have not been run.
  ✗ OK » 1 honored • 1 broken (0.000342s)

topicerror.py

from pyvows import Vows

@Vows.batch
class a(Vows.Context):
    def topic(self):
        return 'a'

    def teardown(self):
        print 'teardown'

    class b(Vows.Context):
        def topic(self):
            return 42 / 0