Brightness/Contrast Node for Cycles

Contrast helps to adjust IBL (HDR images used for background lighting).
Note: In the UI we are caling it Bright instead of Brightness. This copy what Blender composite is doing.
Note2: the algorithm we are using produces pure black when contrast is 100. I'm not a fan of that, but it's a division by zero. I would like to look at other algorithms (what gimp does for example). But that would be only after 2.62.

intern/cycles/blender/blender_shader.cpp

@@ -142,6 +142,10 @@ static ShaderNode *add_node(BL::BlendData b_data, ShaderGraph *graph, BL::Shader
 			node = new GammaNode();
 			break;
 		}
+		case BL::ShaderNode::type_BRIGHTCONTRAST: {
+			node = new BrightContrastNode();
+			break;
+		}
 		case BL::ShaderNode::type_MIX_RGB: {
 			BL::ShaderNodeMixRGB b_mix_node(b_node);
 			MixNode *mix = new MixNode();