Nodes: add absolute value operation to all math nodes

Reviewed By: dingto, brecht

Differential Revision: https://developer.blender.org/D507

intern/cycles/render/nodes.cpp

@@ -3544,6 +3544,7 @@ static ShaderEnum math_type_init()
 	enm.insert("Less Than", NODE_MATH_LESS_THAN);
 	enm.insert("Greater Than", NODE_MATH_GREATER_THAN);
 	enm.insert("Modulo", NODE_MATH_MODULO);
+    enm.insert("Absolute", NODE_MATH_ABSOLUTE);
 
 	return enm;
 }