(setnfsexportent): Set it.
(endnfsexportent, parseopts, getexport, syntaxerr): Use it.
(parseopts): Accept old-style "crossmnt" option, for old xtabs.
(setnfsexportent): Set it.
(endnfsexportent, parseopts, getexport, syntaxerr): Use it.
(parseopts): Accept old-style "crossmnt" option, for old xtabs.