review request (Mx2) 4396719 & 6867958 mark sweep stack overflow

[John Coomes]

This is two requests in one, which may be :-) or :-( depending on your
viewpoint.

The first is for work done by Peter Kessler before he moved to another
group:

	http://cr.openjdk.java.net/~jcoomes/4396719-fat-stack/	

I've simply kept this work up to date and done some additional
testing.  I reviewed his original changes, so one additional reviewer
would be nice.

The second is a follow-on change, which reduces the performance impact
of 4396719 slightly:

	http://cr.openjdk.java.net/~jcoomes/6867958-fat-stack/

It's medium only because it touches many files; the change is very
simple.

-John