Lots of bugs in movestones fixed:

* Movestones no longer eat nodes when running off the track.
* Movestones no longer eat nodes when colliding with an mvps stopper.
* Movestones no longer pass through mvps stoppers.
* Movestones do not eat nodes when they are suddenly placed in the entity's path.
Up/down pistons should also have special rules excluding the pusher side (rotated versions of normal pistons).