'Spawn new worker threads (not above self.max).'

def grow(self, amount):

    for i in xrange(amount):
        if ((self.max > 0) and (len(self._threads) >= self.max)):
            break
        worker = WorkerThread(self.server)
        worker.setName(('CP    WSGIServer    ' + worker.getName()))
        self._threads.append(worker)
        worker.start()
