daemon throttle code could pass values < 0 to sleep()

fixed sleep in daemons throttle code, sleep() only accepts unsigned int but in some cases uWSGI could pass value < 0

I've noticed that if daemon dies right after start I was getting:

```
Mon Oct 14 23:53:40 2013 - [uwsgi-daemons] throttling "my command" for -1 seconds
```

This way sleep() value would overflow and we would wait for very very long time for daemon to be respawned