Keystone 1.3.1

Client fix for Immersive Vehicles. Replace the previous z-keystone jar in the client's mods; the server can stay on 1.3.0.

Signs, poles and vehicles no longer flicker between shaded and bright. Immersive Vehicles draws everything at the
end of the frame and switches lighting on through Minecraft's GL state cache. Other mods that draw at the same moment
and change GL state directly (selection outlines, waypoint beams and similar) left that cache out of step whenever they
had something on screen, and Immersive Vehicles' lighting call was then skipped: its models showed flat and bright in
some frames and shaded in others, changing as the camera moved. Keystone now puts the GL state back in step with the
cache just before Immersive Vehicles draws.