GitLab

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

All platforms now handle nonbonded exceptions in a consistent way (they ignore cutoffs and periodic boundary conditions).  Also started OpenCL implementation of CustomHbondForce.