RFR 8038797: JVMTI FollowReferences does not report roots reachable from nmethods

[Coleen Phillimore]

Summary: Also follow nmethods found on the execution stack.

I have this fix to follow nmethods found on the execution stack but not 
really a good way to test it.  There are two tests internally that 
exercise this code and with some printing, I verified that they do the 
right thing.   I am open to suggestions how to test this, it requires 
compiled methods on the stack with oops that are only referenced from 
said methods in the oop section (not in locals or on stack).

Also ran the tonga colocated/non-colocated internal tests, 
jdk/test/com/sun/jdi.

scp -r /home/cphillim/home/public_html/webrev/8038797.01 
coleenp at cr.openjdk.java.net:
open webrev at http://cr.openjdk.java.net/~coleenp/8038797.01/webrev


thanks,
Coleen