Added scene cache test to check for incremental sample times. Currently failing.
Added scene cache test to check for incremental sample times. Currently failing.

appleseedhq/cortex,appleseedhq/cortex,goddardl/cortex,appleseedhq/cortex,lento/cortex,davidsminor/cortex,danieldresser/cortex,hradec/cortex,goddardl/cortex,lento/cortex,danieldresser/cortex,goddardl/cortex,lento/cortex,hradec/cortex,danieldresser/cortex,hradec/cortex,danieldresser/cortex,davidsminor/cortex,davidsminor/cortex,davidsminor/cortex