RFR: 8242054: Shenandoah: New incremental-update mode

[Roman Kennke]

>> Differential:
>> http://cr.openjdk.java.net/~rkennke/JDK-8242054/webrev.05.diff/
>> Full:
>> http://cr.openjdk.java.net/~rkennke/JDK-8242054/webrev.05/
> 
> I would probably do the diagnostic/experimental mode change separately, but that is your call.

Alright, re-based on top of "8242217: Shenandoah: Enable GC mode to be
diagnostic/experimental and have a name":

http://cr.openjdk.java.net/~rkennke/JDK-8242054/webrev.06/

Good now?

Roman