Make --enable-secure-statd the default.

i.e. you now need --disable-secure-statd if you want any client
other than lockd to talk to statd.

Also relax the RESTRICTED_STATD checks so that a recent kernel
with /proc/sys/fs/nfs/nsm_use_hostnames set can still talk to
statd.

Finally, restrict access to simulate_crash so that only privileged
processes on localhost can call it.  Having it accessible by the
whole world is probably not much more than a minor inconvenience,
but it really should be kept closed.