MFC	r268130, r268224, r268230, r268231:

Various DTrace Merges from OpenSolaris/Illumos:

15-Sep-2008:
6735480 race between probe enabling and provider registration

20-Apr-2008:
6822482 DOF validation needs to handle loadable sections flagged as unloadable

22-Apr-2009:
6823388 DTrace ioctl handlers must validate all structure members

30-Jun-2009:
6851093 system drops to kmdb with anonymous dtrace probes + kmdb

Obtained from:	OpenSolaris