review request - 6784849 part 2 (S)

[John Coomes]

6784849 par compact - can fail when to_space is non-empty

http://webrev.invokedynamic.info/jcoomes/6784849-ddc-enqueue/

This is a follow-on review request to one sent earlier [1] using the
same bug id (6784849).  The earlier changes were incomplete, resulting
in several failures during stress testing.  More detailed comments are
in the webrev.  The failing tests now pass with the current changes.

The earlier changes have already been reviewed; the changes here will
be added to those sent earlier.

-John

[1] http://mail.openjdk.java.net/pipermail/hotspot-gc-dev/2008-December/000663.html