Submitting patch that does not throw an exception, but instead leaves the completion unit in the queue and pulses the lock object if there are any waiting threads. (On the condition when we have "maxcompletionthreads" completion threads.)

This patch actually works! It even solves the race problem between the completion thread loop and the addcompletionitem. It will now only start the minimum number of threads to handle however many simultaneous completion units need to be processed. If this number exceeds the maximum number of threads, it will throw a SystemException.