cross-traffic generation in the delay-agent nodes. These changes need to
be applied to FBSD54-DNODE-PUBSUB and delay-agent files from the PELAB branch
in order to create a working delay node image. "ipfw" must also be recompiled with
this modified Dummynet header.

Added a new parameter to the delay-agent event commands -- "BACKFILL", which
is set similar to bandwidth. Amount of link capacity minus backfill is the desired
available bandwidth.