This experiment extends ALT_INTRA by adding two new modes:
smooth horizontal and smooth vertical.

Improvement on *intra frames* in BDRate (PSNR):
===============================================

AWCY (high latency): -0.46%
(Also, -1.0% or more on PSNR Cb,Cr and APSNR Cb,Cr).

AWCY (low latency): -0.43%
(Also, -0.88% to -0.94% on PSNR Cb,Cr and APSNR Cb,Cr).

Google sets:
lowres: -0.454
midres: -0.484
hdres:  -0.525

Improvement on *video overall* in BDRate (PSNR):
================================================

AWCY (high latency): -0.15%

Google sets:
lowres: -0.085
midres: -0.079

Change-Id: I9f4e7c1b8ded1fe244c72838f336103ccc715d50