Blender Git Loki

CMake build option for security report: CVE-2009-3850
Nothing is changed by default but some linux distributions want to have executing python be opt-in.

This keeps the same functionality but disables auto-run from factory settings and in background mode unless its enabled as a command line argument.

This CMake option is marked as advanced and wont show in the regular options list so its less likely to be enabled by people that like to turn everything ON without reading descriptions :)