presplitting is now available for hair ball and furry ball built-in curve objects.
refactoring.
cosmetics.
moved curve file loading code to new renderer::CurveObjectReader class.

also extended the renderer::CurveObject API.
Merge branch 'master' of github.com:appleseedhq/appleseed
minor tweaks in unit tests.
added missing BSDF models to API header file.