RFR(S): 7111795: G1: Various cleanups identified during walk through of changes for 6484965

[John Cuthbertson]

Hi Everyone,

Can I have a couple of volunteers look over these changes? The webrev 
can be found at: http://cr.openjdk.java.net/~johnc/7111795/webrev.0/

Summary:
During a code walkthrough of the original set of changes for 6484965 
("piggy-back liveness accounting on marking") a few loosely related 
cleanups were identified. I have decided to send these out as a separate 
set of changes.

Testing: the GC test suite and KitchenSink on Solaris and Linux with a 
low marking threshold (10%).

Thanks,

JohnC