first cut for new proc & user structs (still need to put in new vnode calling

first cut for new proc & user structs (still need to put in new vnode calling
convention): get credentials, etc, via proc; u.u_nd, u.u_spare are gone;
purge user.h; consolidate *nullops()

SCCS-vsn: sys/nfs/nfs_node.c 7.30
SCCS-vsn: sys/nfs/nfs_serv.c 7.36
SCCS-vsn: sys/nfs/nfs_srvcache.c 7.10
SCCS-vsn: sys/nfs/nfs_subs.c 7.38
SCCS-vsn: sys/nfs/nfs_syscalls.c 7.25
SCCS-vsn: sys/nfs/nfs_vfsops.c 7.26
SCCS-vsn: sys/nfs/nfs_vnops.c 7.56