[0.8-2054-g0eaaafd] Cannot siphon from a vehicle into a vehicle

What it says on the tin, I don’t know if this functionality was removed intentionally or not but it makes fueling larger vehicles considerably more difficult considering the gas stations have at most four tiles of space between them.

It seems someone decided to refactor and forgot that functionality. Fixed, merge pending. https://github.com/CleverRaven/Cataclysm-DDA/pull/4028