Starting new ColorIllusionSpectra scene to make a Purves-style color illusion with sampled spectra instead of RGB textures.
ColorIllusionSpectrum rendering almost works, but illusion spectrum comes out too dark.
TODO note to self about converting multiple polylists from each mesh in ColladaToPBRT/ConvertGeometry().
Automated two-step rendering for ColorIllusion example scene, and comparing spectra of target and destination pixels.
ColorIllusionSpectra scene scales back on top reflectance and yellow illuminant, to maintain conservation of energy.

Now the illusion works for various top reflecances.
MakeNativePathMappings() allows Mitsuba properties of "boolean" type without trying to convert property name to "filename".
ColorIllusion scene works with realistic or unrealistic computed destination reflectances.
New utility for writing spectrum "spd" files.
Rename ColorIllusionSpectra to SpectralIllusion, revised code for clarity.
SpectralIllusion uses path integrator with 64 samples per pixel.  Looks good.
Remove Mitsuba output file from SpectralIllusion folder.
New version of Interior scene places two dragons in the room.  Also adds large "picture window" area lights.
New "graded" version of the Dragon blends between dragon reflectances, in increments.
WritePBRTFile() flips meshes to be used as AreaLightSources.  I'm not sure if this is always necessary, or when exactly.
Remove SpectralIllusion cruft.
Updated InteriorDragon Blender model with bigger, more visible dragons.
Graded Dragon scene outputs separate images instead of one montage image.
Merge branch 'master' into mappings-refactor