Shorten GF/arf interval in hard scenes.
This patch accounts in the first pass stats for blocks that while not coded as intra, are complex and have an intra error / best error ratio below a threshold. The modification shortens the GF arf interval for a particular class of content that contains a lot of blocks matching the above criteria. (In one short problem test sequence the average interval dropped from about 14-15 to 10-11) The change results in small net gains in metrics results for the Yt(~0.2%) and yt-hd (~0.5%) sets and is approximately neutral for the other test sets. The change is currently shielded by a flag and off by default pending verification that it does not cause other regressions in tests on a wider YT test set. Change-Id: I6b803daa6a4ac09a6f428fb3a18be1ecedd974b7