T8x8 zbin and rate control changes.
Some adjustments to zbin for t8x8. Changes to rules for sizing forced key frames. Some extra stats output in tmp.stt. Approximate gain on YT-hd set 0.5% There are still issues in sizing key frames and gf/arf frames when the image is largely static. These in part relate to problems with cost estimates in the recode loop. Change-Id: I6f0159dc8a8faeab4115a19c668d442491619a68
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