RFR: 8197812: (ref) Data race in Finalizer

[Martin Buchholz]

Embarrassed by my failure to take runFinalizersOnExit into account, I tried
to redo the patch to be actually correct.
 http://cr.openjdk.java.net/~martin/webrevs/jdk/Finalizer-data-race/
even though we may succeed in making runFinalizersOnExit go away, and I'm
not planning to submit any time soon.
The runFinalizersOnExit case needs different mechanics for removing
elements from "unfinalized".
The simple invariant is that you need to run the finalizer whenever an
element is unlinked from unfinalized.