Add option, for newmv-last, to limit the rd-threshold update for early exit,
under a source varianace condition.
This can improve visual quality in low texture moving areas,
like forehead/faces.

Also add bias against golden to improve the speed/fps,
will little/negligible loss in quality.

Only affects CBR mode, non-svc, non-screen-content.

Change-Id: I3a5229eee860c71499a6fd464c450b167b07534d