Disney material improvements and fixes.
Fixed PR comments.
Made white spectrum and lighting conditions globals initialized at the start.
Fixed more PR comments.
Merge pull request #510 from est77/est

Disney material improvements and fixes.
initial version of 'heightfield' devkit sample.
assigned default values to rarely-used arguments.
tweaked formatting.
added foundation::AttributeSet::reserve_attributes().
added renderer::MeshObject::reserve_tex_coords().
reserve texture coordinates before building the mesh, plus a couple simplifications after recent API tweaks.
added incomplete CMake file (missing OpenEXR dependency).
Merge branch 'master' of github.com:appleseedhq/appleseed
cosmetics.
Use search path for simple texture expressions

The path to the texture can be in any subdirectory of the root path
or within any subdirectory of the search path. The relative path to
the texture will be discovered automatically.

Signed-off-by: Marius Avram <marius.avram1309@gmail.com>
Merge pull request #512 from marius-avram/texture_search_paths

Use search path for simple texture expressions