Acceleration on trajectory.
Fix compilation errors and change the profile of ComputeGravitationalAccelerations.
Intrinsic acceleration in integrator.
Take fork time into account.
Trajectory testing.
Better API and more trajectory tests.
Earth-probe test has NaNs.
N-body testing with acceleration.
Fix warnings.
After eggrobin's review.
Merge pull request #132 from pleroy/Acceleration

Support for intrinsic acceleration of massless bodies