minor cosmetic tweak.
Cherry pick FixedEntityModel work.
Small fixes and improvements
Merge branch 'master' of github.com:appleseedhq/appleseed
minor cosmetic tweak.
Merge pull request #465 from est77/est

Added FixedModelEntity, MaterialCollectionItem and other changes needed for GSoC
fixed compilation on Windows.
Merge branch 'master' of github.com:appleseedhq/appleseed
fixed compilation on Windows plus a few fixes and cleanups.