unicast equation-based congestion control added to NS

[Sally Floyd <floyd@aciri.org>]

We (Mark Handley, Jitu Padhye, and myself) have added unicast
equation-based congestion control to the NS simulator.  This code
is described on the web page "http://www.aciri.org/floyd/friendly.html".
Documentation is still in progress, and will be pointed-to on the
web page as it becomes available.

We intend to add multicast equation-based congestion control to the NS
simulator at some point...

- Sally