Physics suckage

Using PyODE instead of a fake dynamics engine means that you have to try to use realistic values to get the behaviour you want. This can leave you with kind of awkward numbers for things like drag and lift.

On the plus side, you don't have to build your own force integrators.

Currently our hang-glider lifts pretty well over steam, but glides a little *too* well on its own power. Gotta work on that.