This unnecessarily blackballs other platforms with good multiprocessing capability (e.g. BSD).Let's fix this for good, relegating to safe PoW just the one known platform not working with fast PoW.

```python
if 'win32' == sys.platform:
    return _doSafePoW(target, initialHash)
else:
    return _doFastPoW(target, initialHash)
```