This to avoids build conflicts with libc++ on FreeBSD, these __ prefixed values
are reserved for compilers. I apologize to anyone who has patches or branches
and has to go through the pain of merging this change, it may be easiest to do
these same replacements in your code and then apply/merge the patch.
Ref T37477.
Node specially useful for Texture correction.
This is also a nice example of a simple node made from scratch in case someone wants to create their custom nodes.
Review by Brecht.
