Cycles / Wavelength to RGB node:

* Added a node to convert wavelength (in nanometer, from 380nm to 780nm) to RGB values. This can be useful to match real world colors easier.

Example render:
http://www.pasteall.org/pic/show.php?id=53202

ToDo:
* Move some functions into an util file, maybe a common util_color.h or so.
* Test GPU, unfortunately sm_21 doesn't work for me yet.

release/scripts/startup/nodeitems_builtins.py

@@ -218,6 +218,7 @@ shader_node_categories = [
         NodeItem("ShaderNodeVectorMath"),
         NodeItem("ShaderNodeSeparateRGB"),
         NodeItem("ShaderNodeCombineRGB"),
+        NodeItem("ShaderNodeWavelength"),
         ]),
     ShaderNewNodeCategory("SH_NEW_SCRIPT", "Script", items=[
         NodeItem("ShaderNodeScript"),