ktr port from FreeBSD

I have ported ktr (kernel trace routines) from FreeBSD (who took it from
BSD/OS).
I will commit it in some days if there are no major issues with it.

FreeBSD also have a ktrdump util which I will commit later.

http://eirikn.kerneled.org/dragonfly/ktr-dfly.patch

-- 
Eirik Nygaard
[e-mail]