reference vfs_check_export
change license to my own, (ok'd by dfr) and remove advert clause.
remove extra Id tags and emacs cruft, this should be a fresh file.
VFS_CHECKEXP.9, now used to check export credentials
VFS_FHTOVP.9, only used for filehandle to vnode, no access checks are done.
VFS.9, inform people of the vfs_std* functions available to avoid
ugly casts to eopnotsup and making of dummy functions to return 0.