odd width support for scale by even scale factor and box scale down by 4.  scale down by 4 uses scale down by 2 internally.
BUG=431
TESTED=libyuvTest.ARGBScaleDownBy4_Bilinear

Review URL: https://webrtc-codereview.appspot.com/57399004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1412 16f28f9a-4ce2-e073-06de-1de4eb20be90