[devel-new-2] Boats get stuck at locks

[Rollmaterial]

sve: https://drive.google.com/file/d/0ByLSSg3gXTz-VWlGb09fazhMNjg/view?usp=sharing
Look at the milk line from Pitlock Cattle Farm.

[jamespetts]

I think that I have managed to fix this one (a very odd bug and hard to track down, since the code that I identified as faulty has been present for a very long time) - would you be able to re-test? I should be grateful.