Change Any functions that convert 1 to 1 formats, memcpy style, so use C for remainder to allow a minimum width of 1.  This has some advantages - allows function to be used even with SIMD that only allows aligned memory.  Fewer macros, used by more functions.  SIMD is not used unaligned avoiding page/cache split.  No overlap so it can be used in place.  Disadvantage is it will be slower if close to the maximum number of non-SIMD pixels.
BUG=373
TESTED=libyuv_unittest still passes
R=brucedawson@google.com, tpsiaki@google.com

Review URL: https://webrtc-codereview.appspot.com/23209004

git-svn-id: http://libyuv.googlecode.com/svn/trunk@1141 16f28f9a-4ce2-e073-06de-1de4eb20be90