RFR(S): Backport 8004816 to hs24

[John Cuthbertson]

Hi Everyone,

Can I have a couple volunteers review the backport to hs24 for this CR? 
The backport webrev can be found at: 
http://cr.openjdk.java.net/~johnc/8004816-hsx24-backport/webrev.0/

The exported changes from hs25 did not apply cleanly to an hs24 
repository (the changes to make the global marking stack dynamic are not 
being backported) and had to be fixed up by hand.

The original hs25 changes can be found at: 
http://cr.openjdk.java.net/~johnc/8004816/webrev.1 and they were 
reviewed by Jon Masamitsu.

Testing:
Kitchensink with a markstack size of 16k, GC test suite with mark stack 
size of 4K.

Thanks,

JohnC