[gclist] Allowing finalizers to wait for the messiah.

[Barry Hayes]

| Prompt. Your job doesn't have to run a billion years to
|         get its finalizers run. You aren't running one
|         finalizer per collection cycle.

"Prompt" is in direct collision with our current ability to write generational
collectors. As long as I have a generation of objects that I'm not going to
collect any more often than once per messianic era, I either can't put
finalizable objects in that generation [which restricts the collector and
creates overhead as finalizable objects clog the young generations] or it just
won't get finalized "promptly."