In some case, flux-adding and LART does not agree with each other. (emission w/ scattering)

[HajimeKawahara]

In tests/integration/unittests_long/twostream/twostream_spectrum_test.py (emission w/ scattering) , flux-adding and LART agree well with each other, but in some case, I found they gave different results and I do not why. See Jupiter_cloud_model_using_amp_debug.py when I was developing the mieclouds implementation. I postpone this issue to the future fix because mieclouds focuses on a scattered light spectrum.