The cause is an unknown node socket type in node groups. Ideally the node system
should handle this better and remove the unknown sockets from groups, but this
is a bit of a risky fix to do now, so instead the shader socket type has been
added, since this is a simple change and the code has been tested well.
The reason was that group nodes tried to reconstruct sockets from the template lists, which are empty. Now the verification function checks if there are any sockets in the template lists, which are always empty for group nodes.
This branch adds mostly organizational improvements to the node system by renaming the node folders and files. A couple of internal features have been added too.
Detailed information can be found on the wiki page:
http://wiki.blender.org/index.php/User:Phonybone/Particles2010
