vkernel - Restabilize pmap code, redo kqueue, systimer, and console code

vkernel - Restabilize pmap code, redo kqueue, systimer, and console code

* Remove vm_token and add necessary vm_page spin locks to the vkernel's
  pmap code, improving its stability.

* Separate the systimer interrupt and console tty support from the
  kqueue subsystem.

  Uses SIGURG for systimer
  Uses SIGIO for kqueue
  Uses SIGALRM for cothread signalling

* The vkernel systimer code now uses a dedicated cothread for timing.  The
  cothread is a bit of a hack at the moment but is a more direct way of
  handling systimers.

* Attempt to fix user%/sys%/intr%/idle% in the systat -vm and
  systat -pv output.  Still isn't perfect, but it is now more
  accurate.