Preview Render:
* Changing Material Preview type (Sphere, Monkey...) should not trigger ND_SHADING_DRAW. Caused Cycles 3D View render to re-start. 

It now only triggers an ND_SHADER update, which will be handled inside the Properties Editor Listener and executes a Preview Re-Render. 

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54187 954f8c5b-7b00-dc11-b283-0030488c597c