Make module level loggers process aware

Fixes #1330.

The pull request contains two commits:
* one for Python 2.x and 3.x unification (in suggestion we do not support Python 3.0)
* one that fixes the issue with logging

The second commit doesn't fix the issue for all possible configurations, but it works in assumption we use loader that discovers tasks in loader's import_default_modules (djcelery works this way).

I've also removed parameter colorize in Worker's setup_logging, which seems to be never used (review is required though).

This pull request is a successor of #1331.