Computer Science 360
                             Assignment 8
                         Due 11:59 PM April 18

In this assignment you will implement the rps_close() function
in rpsapi.c and add rps_rcvcls() and rps_rcvclack() to the
receiver system.

The main "challenge" in close is ensuring that both sender and
receiver rings are completely drained before they are shutdown
and return is made to the application.

Evidence of improper close is typically failure to send/receive
the last few packets in a high speed transfer.