RFR (XXS): 6904858: G1: Disable ReduceInitialCardMarks feature for G1

[john cuthbertson - Sun Microsystems]

Hi Everyone,

Can I have a couple of volunteers look at the change for this CR? The 
webrev can be found at http://cr.openjdk.java.net/~johnc/6904858/webrev.0/.

Basically we  turn off the ReduceInitialCardMarks for G1 to match the 
behavior in previous releases so that the fix for 6902115 can bake for a 
while longer.

Thanks,

JohnC