use IS_ALIGNED for width and stride to avoid mod that generates 6 instructions
BUG=none
TEST=disassemble to confirm smaller/simplier alignment checks
Review URL: http://webrtc-codereview.appspot.com/287001

git-svn-id: http://libyuv.googlecode.com/svn/trunk@91 16f28f9a-4ce2-e073-06de-1de4eb20be90
7 files changed