RFR(M): 8212243: More gc interface tweaks for arraycopy and some other smaller changes in preparation for Shenandoah

[Roland Westrelin]

Hi Vlaimir,

Thanks for looking at this. Here is a new webrev that isolates the array
copy related changes and implements your suggestions:

http://cr.openjdk.java.net/~roland/8212243/webrev.01/

Roland.