kernel - Refactor the lwkt_token code, making it faster

kernel - Refactor the lwkt_token code, making it faster

* Rewrite the core token functions and revamp the structures.  The
  lwkt_token structure now contains just a single element, a pointer
  to the on-stack lwkt_tokref.  The lwkt_tokref now contains the
  owner id.

* Recursive tokens are still fully supported and coded trivially.

* Critical sections and spinlocks are no longer needed or used by
  the lwkt_token code.  Token aquisition is basically a single
  atomic_cmpset_ptr() call in the critical path.  Everything runs
  ultra clean now.

* Improve the pool token API.

* Remove extranious cruft