request for review (S): 6814943: getcpool001 catches more than one JvmtiThreadState problem

[Keith McGuigan]

This closes a race condition hole between  
JvmtiThreadState::state_for_while_locked() and ~JavaThread().  Without  
this, the state_for_while_locked() could see a value of false for  
thread->is_exiting(), then the entirety of ~JavaThread() could run,  
the state_for_while_locked() could then finish leaving the  
JvmtiThreadState referring to a zombie thread.

webrev: http://cr.openjdk.java.net/~kamg/6814943/webrev.00/

Thanks for any review!

--
- Keith