[PATCH] Add locking to aha(4)

I have patches to add locking to aha(4) and mark it MPSAFE.  The patches are 
from HEAD but should apply to 8 or 9.  If you test it on 8 or 9 please enable 
INVARIANTS for at least the initial testing.  Thanks.

http://www.FreeBSD.org/~jhb/patches/aha_locking.patch

-- 
John Baldwin