par compaction review requests - 6784849 (XS), 6786188 (S)

[John Coomes]

6784849: par compact - old/new address assertions are too strong

	http://webrev.invokedynamic.info/jcoomes/6784849-relax-assert/

	Change the assertions that check before compaction/after
	compaction addresses to handle the case when data is moved
	from a space at lower addresses to a different space at higher
	addresses.  Currently, this only occurs with the survivor
	spaces, when to_space < from_space.

6786188: par compact - "SplitALot" stress mode should fill to_space

	http://webrev.invokedynamic.info/jcoomes/6786188-splitstress2/

	Update ParallelOldGCSplitALot so compaction occasionally sees
	objects in both from_space and to_space.  This helped diagnose
	6784849.

Neither of the above affect any product code.

-John