Pull up following revision(s) (requested by hannken in ticket #702):
sys/miscfs/procfs/procfs_vnops.c: 1.203
Lock the target cwdi and take an additional reference to the
vnode we are interested in to prevent it from disappearing
before getcwd_common().
Should fix PR kern/53096 (netbsd-8 crash on heavy disk I/O)

(snj)