Merge https://github.com/appleseedhq/appleseed
Merge https://github.com/appleseedhq/appleseed
Add ability to assign materials to both sides of an object instance at once
Merge pull request #342 from est77/master

Moved closures test scene to its own directory.
modified spectral widget to use custom wavelengths from input
fixed crash on Linux.

When setting the format of an input to renderer::InputFormatSpectrum, the input evaluator will write a (spectrum, alpha) pair, not just a spectrum.
Merge branch 'master' of github.com:appleseedhq/appleseed
fixed uninitialized input values when no source was bound to an input.
assign default value 0.0 to the translucency input of the physical surface shader.
Merge https://github.com/appleseedhq/appleseed
avoid changes to object instance
Merge pull request #338 from DaviesX/master

Add ability to assign materials to both sides of an object instance at once
code simplifications and cleanups.
modifying the code to be safe for DLL exports
still some more modifications
some more changes
Modifying the code to be safe for DLL exports
fixed bug introduced in dcc8dd353ee6d50a10f8d45c2d1875cd4d46430b.

don't try to generate side="both" when emitting material assignments.
the front/back material mappings of an object instance are now mutable.
be stricter about assignment of materials to slots when the object defines a single slot.

we now require that slot names used in material assignments always match exactly slot names declared by objects (except when objects don't declare any slot, in which case any slot name will do in material assignments).

before this commit, when an object defined a single slot, material assignments could use any slot names.

added a migration step to maintain backward compatibility.