Revised mRGBEinit() to adjust range minimum as a function of the normalisation factor. This is because sign reversals occurred with higher normalisation values. This is happened when offsetting by the minimum in mRGBEencode() falls below mRGBE_MIN, which is then clamped to zero since it lies beyond the mRGBE encoding's resolution; negatives signs were then lost under these circumstance. Also PMAP_CONTRIB_JITTERZEROS to test breaking up compression artefacts in the reconstructed contribs. This basically added high frequency noise, but didn't help reduce the artefacts, primarily because they are dependent on the frequency in the wavelet domain.