API changes in master branch

[scpeters]

As an FYI to other users, the recently merged #363 made some API changes.

In f4b0cc8 for example, the btHinge2Constraint class is changed to derive from btGeneric6DofSpring2Constraint instead of btGeneric6DofSpringConstraint. The main issue is that now the getRotationalLimitMotor function returns type btRotationalLimitMotor2 which does not inherit from btRotationalLimitMotor. We can work around this with ifdef's if backward compatibility can't be achieved.

[erwincoumans]

The btGeneric6DofSpringConstraint is going to be deprecated and removed in the future. Is there a particular feature/API thing missing from the new btGeneric6DofSpring2Constraint and/or btRotationalLimitMotor2? Thanks for the feedback!

[scpeters]

I haven't checked for missing features. I was just noticing a failed gazebo build, so we'll probably have to use ifdef's until bullet 2.83 is available on Ubuntu platforms.

[bchretien]

👍 Gazebo compilation is currently broken on Arch Linux (Bullet 2.83) because of this.