Conveyer lifts: unsupported conveyers should be allowed

When you drag a belt specifically between conveyer lifts, though codewise it should apply to all conveyor ports in this game, there should be no support pillars required if the span is the same length as the allowed 'unsupported' span between towers.
This will allow you to send belts between conveyor lifts at their max height, and in rare cases like a deep hole and 2 buildings, it would let the belt span the chasm.
This is physically realistic - if a belt can go between 2 towers at +3 height, it should be able to do this at any height if no pillars are required.

I think this problem can be fixed if the lift is considered as a "pillar" when building conveyors