Cycles: make multiple importance sampling for lamps an option per lamp now,
disabled by default for backwards compatibility.
http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/Integrator

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54210 954f8c5b-7b00-dc11-b283-0030488c597c