RFR: Correctly iterate references in humongous regions

[Aleksey Shipilev]

On 03/31/2017 12:50 PM, Roman Kennke wrote:
> http://cr.openjdk.java.net/~rkennke/oop-iterate-humongous/webrev.00/

This makes me a little itchy:

 547     while (! region->is_humongous_start()) {
 548       region = _ordered_regions->get(region->region_number() - 1);
 549     }

Rewind could use a simple local var?

Otherwise good.

-Aleksey