Add additional high bridge tile sets

[Blade]

Bridge sets use special logic and so can't have additional sets created in the TX or mod specific terrain expansions without additional support from the executable. This is required to implement high train bridges as in TS amongst other things.

[pd (pdmail)]

Ah yeah, I remember jonwil having a try there.

[Nikademis Von Hisson (nikademis-von-hisson)]

Is this something to fix the train bridges?

[Blade (nadia-xy)]

In theory, it will allow train bridges as well as other additional high bridge graphics.