Introduced back when I added a "last-hop" queue to allow prioritized
messages to go to the front of the set of msgs loggp is to receive. Haven't yet
put it in other models (simple*), so RNG bug doesn't affect there yet.

same var name used for the "sequencing" macros

doesn't support IO operations

Tired of explaining that it's not a good representation of a WAN. Instead, it's
now a simple point-to-point latency/bandwidth model.

NOTES:
- torus does not use it, as it has some routing logic preventing direct usage.
  It probably can be done, but I'll leave that for later.
- collectives in torus, dragonfly don't use it yet.

(have NO idea how the triton tests passed without this...)