FTweaks Cargo Ships Incompatibility Fix

[Pixelguru26]

FTweaks is incompatible with Cargo Ships due to a modification performed on rail signals in line 30-31 of prototypes/overrides.lua removing the "rail-layer" collision mask. Adding "rail-layer" back into the list fixes the incompatibility, however I don't know if that's a viable option as I do not know the reasoning behind changing the rail signal collision mask at all.

[ReikaKalseki]

The reasoning behind the change was to make the signals useful alongside rail bridge mods. I can remove that line, though, as its benefit is small.