libyuv

Neon 38 downscaler.

Fixed up unit tests for filters to use same image generation and comparison code.

Added timing information output from doing scale.
Review URL: http://webrtc-codereview.appspot.com/244016

git-svn-id: http://libyuv.googlecode.com/svn/trunk@48 16f28f9a-4ce2-e073-06de-1de4eb20be90