cache_lookup() has returned a ref'ed and locked vnode since
vfs_cache.c:1.96, dated Tue Mar 29 12:59:06 2005 UTC. This change
is similar to the change made to smbfs_lookup() in smbfs_vnops.c:1.58.
Tested by: "Antony Mawer" ant AT mawer.org
MFC after: 2 weeks