SceneCacheTest: Add test for curve and point writing.
SceneCacheTest: Add test for curve and point writing.

- Add test to verify we correctly raise an error when
writing out an scc from a mix of curve primitive and free
floating points ( without a particle system )
- Prefer functools.partial over IECore.curry for all test

appleseedhq/cortex,appleseedhq/cortex,appleseedhq/cortex