pass indication of idempotency through to the nfsm_request routine;

pass indication of idempotency through to the nfsm_request routine;
in remove, unlock parent directory first to avoid deadlock with
removal of silly rename file on final vrele;
map ENOENT on rename, and EEXIST on link, symlink, and mkdir to zero
as they would have been detected on lookup, so come about because
of non-idempotency on retries

SCCS-vsn: sys/nfs/nfs_vnops.c 7.26