Added WAVELET_TEST_mRGBE option to the unit test in wavelet2.c. This tests the mRGBE encoding of wavelet coeffs and how their inverse xform compares to the original (and to that with the non-encoded coeffs). So far the results have been encouraging; artefacts from mRGBE encoding are less significant than those from high compression rates. Also added another monotonic input data initialisation, this time with linearised (1D) bin values.