Fix TypeError with Python 2.6 and Plone.

- Add test buildout for Plone 4.2 with Python 2.6
- Fix TypeError with Python 2.6 and Plone:
  ```python
  TypeError: super() argument 1 must be type, not classobj
  ```

   The logging.Handler is not a classobj in python 2.6, so we can't use super.