- tox now uses the Zope test runner to execute tests, since setup tests cannot
  deal with layers, especially when they need to spawn sub-proceeses.

- Switched all functional tests to use `WebTest` instead of
  ``zope.testbrowser``. Setup proper layering.

- Do not rely on ``zope.testbrowser.wsgi`` WSGI layer support. It was not
  needed anyways.

- Minimized the ``ftesting.zcml`` setup.
- You can now specify additional WSGI middleware components wihtout
  subclassing the ``BrowserLayer`` class.

All tests pass now.
Preparing release 4.0.0a3
Back to development: 4.0.0a4