Fixed #513

Quoting from #513:

> Some exceptions in test generators make nosetests-3.X produce unhelpful traceback:

> ```
> $ nosetests-3.2 --version
> nosetests-3.2 version 1.1.2
> $ nosetests-3.2 test.py
> E
> ======================================================================
> ERROR: Failure: UnicodeEncodeError ('ascii' codec can't encode character '\xf1' in position 0: ordinal not in range(128))
> ----------------------------------------------------------------------
> Traceback (most recent call last):
>   File "/usr/local/lib/python3.2/dist-packages/nose-1.1.2-py3.2.egg/nose/failure.py", line 37, in runTest
>     raise self.exc_class(self.exc_val).with_traceback(self.tb)
> TypeError: function takes exactly 5 arguments (1 given)
>
> ----------------------------------------------------------------------
> Ran 1 test in 0.002s
>
> FAILED (errors=1)
> ```

> Test case: https://gist.github.com/2392839

This PR fixes this bug and attemps to not cause other issues :)