IJG JPEG 7+ uses a different upsampling algorithm which produces
different numeric results.
* libtiff/tif_jpeg.c (JPEGPreDecode): Patch from Even Rouault to
work with IJG JPEG 7+.
The test case was ignoring the documented API for TIFFReadRGBATile,
namely that the output pixels are uint32's and the macros TIFFGetR etc
should be used to fetch the pixel components.
Original patch by Marcus Meissner, somewhat cleaned up by me.