Revised adjustment for rd based on source complexity.
Two cases:
1) Bias against low variance intra predictors
when the actual source variance is higher.
2) When the source variance is very low to give a slight
bias against predictors that might introduce false texture
or features.
The impact on metrics of this change across the test sets is
small and mixed.
derf -0.073%, -0.049%, -0.291%
std hd -0.093%, -0.1%, -0.557%
yt +0.186%, +0.04%, - 0.074%
ythd +0.625%, + 0.563%, +0.584%
Medium to strong psycho-visual improvements in some
problem clips.
This feature and intra weight on GF group length now
turned on by default.
Change-Id: Idefc8b633a7b7bc56c42dbe19f6b2f872d73851e
7e234b9228