kernel - Add usched_dfly algorith, set as default for now (3)

kernel - Add usched_dfly algorith, set as default for now (3)

* Add a field to the thread structure, td_wakefromcpu.  All wakeup()
  family calls will load this field with the cpu the thread was woken
  up FROM.

* Use this field in usched_dfly to weight scheduling such that pairs
  of synchronously-dependent threads (for example, a pgbench thread
  and a postgres server process) are placed closer to each other in
  the cpu topology.

* Weighting:

  - Load matters the most
  - Current cpu thread is scheduled on is next
  - Synchronous wait/wakeup weighting is last

* Tests on monster yield better all-around results with a new all-time
  high w/ pgbench -j 40 -c 40 -T 60 -S bench:

  25% idle at 40:40 tps = 215293.173300 (excluding connections establishing)

  Without the wait/wakeup weighting (but with allwload and current cpu
  weighting):

  41% idle at 40:40 tps = 162352.813046 (excluding connections establishing)

  Without wait/wakeup or current-cpu weighting.  Load balancing only:

  43% idle at 40:40 tps = 159047.440641 (excluding connections establishing)