Change coefficients for the rangecompress/expand transformation.

It's a bit of a tradeoff, but the high lords of color and image processing
say that these are better for real-world cases.

The only down side is that the previous coefficients did not change values
that were < 1 at all, so LDR images going through a compress-filter-expand
loop were truly identical to the filtering alone -- changes only happened
in the filter neighborhood of true HDR values.  The new coefficients
will make LDR images behave ever so slightly differently with range
compress/expand than without, but I've tried some examples and the change
is not visually noticable for LDR images, but for HDR images the behavior
around the highlights is superior with the new coefficients.