I saw that you added the contributed Character class (it was actually by "SomethingNew" and not by me) but I did not receive any feedback when I contacted you so I have set up my own branch of your bullet port here. I sync it with your mtn version from time to time.
This branch is used in jMonkeyEngine3 for the physics simulation. It adds a HeightfieldTerrainShape contributed by the same guy and a maxForce parameter for the vehicle (as in the latest bullet version). If you care to add anything from this branch, its at your disposal.