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.

source/blender/makesrna/intern/rna_material.c

@@ -114,7 +114,7 @@ static void rna_Material_update_previews(Main *bmain, Scene *scene, PointerRNA *
 	if (ma->nodetree)
 		ntreeClearPreview(ma->nodetree);
 		
-	rna_Material_update(bmain, scene, ptr);
+	WM_main_add_notifier(NC_MATERIAL | ND_SHADING, ma);
 }