There is no more TAILQ fifo to harvest the entropy; instead, there
is a circular buffer of constant size (changeable by macro) that
pretty dramatically improves the speed and fixes potential slowdowns-
by-locking.
Also gone are a slew of malloc(9) and free(9) calls; all harvesting
buffers are static.
All-in-all, this is a good performance improvement.
Thanks-to: msmith for the circular buffer concept-code.