GitLab

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

Simplified constraint code.  In the process, this fixed a bug that caused bubbles to appear in water when running on Fermi GPUs.

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

Fixed bug where MonteCarloBarostat would leave molecules seeming to be outside the first periodic box

Exported some symbols from Cuda plugin, for use by external NML plugin.
  cudaOpenMMInitializeIntegration, gpuSetConstants, CudaPlatform
  (but I couldn't figure out how to export kGenerateRandoms)
Also turned off TestRandomCuda on Windows, since it always fails and makes the dashboard look bad.
Renamed InitializeIntegration method to cudaOpenMMInitializeIntegration, now that symbol is being exported.

Use a consistent (and more accurate) value for electric constant everywhere.  Also cleaned up handling of constants and units in various places.