page fault in propagate_priority

I've gotten the following panic twice in the last few days.  I'm pretty
sure truss has something to do with it, since I just started trussing
something when it paniced.  No crashdumps unfortunately, and the system
locks up hard so I have to reset it.

The fault address is 0x24 so it looks like a null pointer dereference
of some sort.  I've added asserts to propagate_priority any place a
pointer to a structure is dereferenced, so if it happens again I should
have the line number at least.

panic1 was on an Oct 15 kernel, panic2 was on an Oct 27 kernel.

-- 
	Dan Nelson
	dnelson_at_allantgroup.com