clean noise from worker pool

[plastikfan]

Whilst the worker pool is in development phase, there are a lot of print statements embedded within its implementation, for debugging purposes. However, this is clearly not to remain for production code. When the worker pool has been fully implemented and has demonstrated stability, all print statements should be removed. It might be that we can define hooks that a test client can use to embed print statements so that they are not in the core functionality.