Cycles / Blackbody to RGB node:

* Added a node to convert a temperature in Kelvin to an RGB color. This can be used e.g. for lights, to easily find the right color temperature. 
= Some common temperatures =
Candle light: 1500 Kelvin
Sunset/Sunrise: 1850 Kelvin
Studio lamps: 3200 Kelvin
Horizon daylight: 5000 Kelvin

Documentation: http://wiki.blender.org/index.php/Doc:2.6/Manual/Render/Cycles/Nodes/More#Blackbody

Thanks to Philipp Oeser (lichtwerk), who essentially contributed to this with a patch! :)

This is part of my GSoC 2013 project. SVN merge of r57424, r57487, r57507, r57525, r58253 and r58774

intern/cycles/render/svm.cpp

@@ -398,6 +398,10 @@ void SVMCompiler::generate_svm_nodes(const set<ShaderNode*>& nodes, set<ShaderNo
 							inputs_done = false;
 
 				if(inputs_done) {
+					/* Detect if we have a blackbody converter, to prepare lookup table */
+					if(node->has_converter_blackbody())
+					current_shader->has_converter_blackbody = true;
+
 					node->compile(*this);
 					stack_clear_users(node, done);
 					stack_clear_temporary(node);
@@ -672,6 +676,7 @@ void SVMCompiler::compile(Shader *shader, vector<int4>& global_svm_nodes, int in
 	shader->has_surface_emission = false;
 	shader->has_surface_transparent = false;
 	shader->has_surface_bssrdf = false;
+	shader->has_converter_blackbody = false;
 	shader->has_volume = false;
 	shader->has_displacement = false;