This is added in the spirit of the general cycles GLSL system
which is pretty much WIP still.
This will only work on cycles at the moment but generating for blender
internal is possible too of course though it will be done in a separate
commit.
This hasn't been tested with all and every node in cycles, but
environment and regular textures with texture coordinates work.
There is some difference between the way cycles treats some coordinates,
which is in world space and the way GLSL treats them, which is in view
space.
We might want to explore and improve this further in the future.
...also </drumroll>
