Adding "preferPhysical" parameter to Game::getGamepad().
Using this to simplify the tests that use gamepads.
Fixing some issues related to adding and removing gamepads.
Allowing for multiple virtual gamepads within a game's configuration.
Updating the lua bindings.
Removing USE_XINPUT from project settings.
Merge pull request #728 from ablake/next

Fixing stuff.
Hide Bullet dependency by making PhysicsMotionState private.