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