kernel - Change fill_kinfo_lwp() and fix top

kernel - Change fill_kinfo_lwp() and fix top

* Change fill_kinfo_lwp(), an internal function used by kern_proc.c
  and libkvm, to aggregate lwp data instead of replace it.

  Note that fill_kinfo_proc() will zero the lwp sub-structure and is
  already typically called before zero or more fill_kinfo_lwp() calls,
  so the new aggregation essentially just works even though the API is
  a bit different.

  In addition, when getprocs is told to aggregate lwps the tid field
  will be set to -1 since it is not applicable in the aggregation case.

* 'top' will now properly aggregate the threads belonging to a process
  when thread mode 'H' is not in effect.

* Also allow top to display cpu percentages above 100%, since in the
  aggregation case the sum of threads can easily exceed 100% of one core.

Requested-by: hsw