When the experiment is ON, we use Paeth predictor instead of TM
predictor.

For derf set, this gives about 0.09% improvement overall, and 0.55%
improvement if all frames are forced to be intra-only.

Also, if the EXT_INTRA experiment is also on, the improvement overall
is 0.056%, and improvement if all frames are forced to be intra-only is
0.465%.

Change-Id: Id74e107ede70a8d2107fa14fcb3f44b23a437274