changes:
Atom types can now define custom adjacency code for the smoothing system.
Walls now draw using the generic icon smoothing system.
Walls now pre-bake colors into their icons instead of doing it client-side with the color var.
Walls can now use the SSoverlay appearance cache; wall icon updates should be faster.
The "rusty" wall type now actually works.
Smoothing now uses mutable_appearance instead of image in some places.
Should be a bit easier on clients, though I haven't done profiling.
This PR breaks 510 compatibility.
41e39f52d1