Fix RGB565ToARGB_Any which uses SSE2 that requires ARGB alignment.  Add row coalescing to convert_argb.cc.  Improve coalescing on planar_functions.cc and convert_from_argb.cc.  Use stride * 2 == width to test for even width.  Apply coalescing to all functions that have same vertical subsampling.
BUG=197
TESTED=libyuv unittest passes where _Opt uses row coalescing.
Review URL: https://webrtc-codereview.appspot.com/1186004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@601 16f28f9a-4ce2-e073-06de-1de4eb20be90