Add forward_overlap and backward_overlap to RollingStockPrototype

[Subject314159]

Well let's just say I have a.. rather peculiar.. mod idea, where I have a train that has overlapping carriages. Due to the game's rendering engine (from left to right and from top to bottom) this train is rendered properly when facing towards the right, but messes up when facing towards the left.

You might recognize this "train"

All segments are rendered in the correct order when facing right


The segments are rendered in the order of the rendering engine but it just looks awful when facing left

With the introduction of demolishers the SegmentPrototype has the forward_overlap and backward_overlap properties. It would be great if we could also have this on RollingStockPrototype.

[eugenekay]

...can you please upload a copy of this Mod "as-is"? I don't know if it would be useful for actually implementing this Request to the Devs, but I would very much like to give this innovative Train Design some trial runs.