Distinguish the 3 different methods for acquiring pixel color values (executePixel, executePixelSampled, executePixelFiltered).
This makes it easier to keep track of the different sampling methods (and works nicer with IDEs that do code parsing).
Differential Revision: http://developer.blender.org/D7
Think should be pretty much harmless since if this node was used for buffers
with infinities it already showed artifacts. Now it should be more useful for
mapping Z buffers.
this node allows for more control for normalization of the mapped input range.
Made during BlenderPRO 2012 - Brasilia, Brazil :)
Idea and testing: Daniel Salazar
Implementation: yours truly
Reviewed by Lukas Toenne and Sergey Sharybin
