Cycles: ray visibility options now work for lamps and mesh lights, with and without
multiple importance sampling, so you can disable them for diffuse/glossy/transmission.

The Light Path node here is still weak and does not give this info. To make that
work we'd need to evaluate the shader multiple times which is slow and we can't
detect well enough when it is actually needed.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57284 954f8c5b-7b00-dc11-b283-0030488c597c