* scalar optimization, vectorization. * 1.7% AEC overall speedup for the straight C path. * 12.2% AEC overall speedup for the SSE2 path. Review URL: http://webrtc-codereview.appspot.com/88006 git-svn-id: http://webrtc.googlecode.com/svn/trunk@253 4adac7df-926f-26a2-2b94-8c16560cd09d