Fix an unsafeness with the hop-to-next-page thing; SANDmark 30.
Fix an unsafeness with the hop-to-next-page thing; SANDmark 30.

Specifically, the dependency of the part before the boundary on the part
after wasn't registered, because there's no way to do that yet, so a
shootdown of the second part would still leave the first part live and
able to fall through into the stale code.



jld/umx,jld/umx