~3-5% faster encoding optimizing PickBestIntra*()

* Add early-out check for Intra16
* replace some memcpy() by pointer swap

Change-Id: I5edc5f7fbc8e39984deb48e6c045c97c61418589
Merge "~3-5% faster encoding optimizing PickBestIntra*()"
enc/histogram.c: reindent after f4059d0

fixes indent in HistogramRemap after:
f4059d0 Code cleanup for HistogramRemap.

Change-Id: I9f53a088749e9100a70331bda1662488666c5156