tests: Fix processing tests on Windows. See the comment in `pipeline.py` for more info but basically I was passing already initialized processors to the worker pool, which means pickling the whole app. Pretty bad. Interesting that it only broke on Windows, though.

sudo: false
language: python
python:
  - "3.4"
install:
  - "pip install -r requirements.txt"
  - "pip install -r dev-requirements.txt"
script: py.test