NaCL pepper_33 port of scale and compare using lock/unlock.  Remove less useful scaling tests and change default size to a multiple of 16 for better assembly coverage.
BUG=none
TESTED=ncval
R=nfullagar@google.com

Review URL: https://webrtc-codereview.appspot.com/5939005

git-svn-id: http://libyuv.googlecode.com/svn/trunk@917 16f28f9a-4ce2-e073-06de-1de4eb20be90