Take into account network congestion

This does something simple for congestion management: it just reserves
a new network routing instruction at each point in time and uses that
to foward on to the next cycle.
Add support for registers (clock_lo only)

This schedules a read of all registers but doesn't schedule the write.
I figure it's good enough for now...
Add a SIFT benchmark

Despite being the largest SIFT benchmark this is still pretty small
compared to DES...