Attempt to improve performance by refactoring the compression-side color conversion and DCT algorithms so that they take full advantage of the additional registers available with 64-bit SSE2.  This produces a somewhat yawn-worthy speedup of 2-3%, but at least the code is a lot more readable now.


git-svn-id: svn://svn.code.sf.net/p/libjpeg-turbo/code/trunk@1335 632fc199-4ca6-4c93-a231-07263d6284db