Since ImageMagick 6.8.1, compare returns 1 for images that are not the same, instead of always returning 0, since there is no exception.
Update tests to account for small variances in compare result due to metric changes in IM versions.
Update all images to be PNGs instead of JPEGs.  Should prevent tests from incorrectly failing across IM versions due to weird changes in JPEG compression.
Resize wasn't testing MODE_RESIZE_ABSOLUTE.
Change test_image_3.png to be a JPEG.  Since I made everything a PNG, it wasn't testing the convert from JPEG path any more.