In addition to `NO', which disables programs, I've added another magic
value for all of the foo_flags variables: `DEFAULT'.  This enables a
program using the `default' flags, whatever they happen to be.  This
way, most users can just enable the programs they want without having
to know what the flags mean.

This change modifies the semantics of `nfsd_flags' and `nfsiod_flags'
in an incompatible way.  Before, if these variables were empty, they
got the default flags; now, if they are empty, then no flags will be
passed to the corresponding program.

Also, I deleted the `amd' variable; you can turn off amd by setting
`amd_flags' to `NO'.  This is also incompatible, in that `amd_flags'
was previously empty by default.

So, if you install a new rc, make sure you either copy in the new
rc.conf, or change `nfsd_flags', `nfsiod_flags', and `amd_flags' in
your copy as appropriate.