Blender Git Loki

Fix for OSL memory leak. The context creation for OSL is now done in the shader_setup_* functions, since it should specific to the sample being worked on. The the context release then happens in the kernel_shader functions after shader evaluation is done. Care has to be taken to ensure the shader_release function is also called in cases where the path integration is cancelled early, this was the main cause for unreleased contexts and subsequent new allocations.