Pull up following revision(s) (requested by hannken in ticket #1094):
sys/nfs/nfs_vnops.c: revision 1.309
Return an error if NFSPROC_LOOKUP returns the file handle of the current
directory.  Treating it as DOT lookup would put garbage into the name
cache and could panic on future lookups.
Seen with ZFS file system exported from OmniOS, an OpenSolaris derivative.
Fixes PR kern/50664 "cd .." over NFS/ZFS can panic kernel

(snj)