Also extend intra pred speed test to rectangular block.
Speedup (i7-6700)
predictor      sse2 v. C
left 4x4       ~5.6x
top  4x4       ~7.2x
128  4x4       ~6.9x
left 4x8       ~7.7x
top  4x8       ~10.1x
128  4x8       ~10.0x

left 8x4       ~8.1x
top  8x4       ~9.1x
128  8x4       ~10.1x
left 8x8       ~10.3x
top  8x8       ~13.6x
128  8x8       ~14.8x
left 8x16      ~12.6x
top  8x16      ~14.0x
128  8x16      ~15.5x

left 16x8      ~6.3x
top  16x8      ~7.0x
128  16x8      ~6.5x
left 16x16     ~6.5x
top  16x16     ~7.1x
128  16x16     ~8.2x
left 16x32     ~5.1x
top  16x32     ~6.4x
128  16x32     ~5.6x

left 32x16     ~4.2x
top  32x16     ~4.3x
128  32x16     ~4.5x
left 32x32     ~3.8x
top  32x32     ~3.7x
128  32x32     ~3.9x

Change-Id: Ie7fcc85b9ded3030ee904623c40e9edeec1695ae