recv-side queuing support (loggp only)
Rather than model-net LPs directly sending messages to other model-net LPs, LPs can route the intended message through the scheduler interface to be queued up for reception by the receiver (see the diff of loggp.c). This has the benefit of enabling things like priority and fairness for N->1 communication patterns. Currently, no packetizing is supported, and I haven't yet wrote checks for it - beware. Loggp is currently the only supported model. simplenet could also be supported without much trouble, but I doubt there's any demand for it at the moment. This should NOT be used by the dragonfly/torus models, as they have their own routing backend.