bullet: properly find Bullet::Dynamics.
bullet: properly find Bullet::Dynamics.

When this was missing, a subproject setup didn't work, complaining about
Bullet::Dynamics not existing.

mosra/magnum-examples,mosra/magnum-examples,mosra/magnum-examples,mosra/magnum-examples,mosra/magnum-examples,mosra/magnum-examples,mosra/magnum-examples