GitLab

When computing kinetic energy, make sure the shifted velocities are perpendicular to the constraints

Variable time step integrators correctly report the size of the last step taken.  Also improved accuracy of integration unit tests.

NonbondedForce sometimes included energy terms that weren't appropriate to the specified force groups

Refactored ForceImpl, lots of KernelImpl subclasses, and other related classes to avoid redundant calculations when requesting a State with both forces and energies