GitLab

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

Fixed Linux compilation error.  Since dlopen() doesn't support RTLD_FIRST on Linux, both plugin initializer functions are now mandatory.

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

Added a version of Platform::getPlatform() that looks up platforms by name.  Added a Context constructor that allows platform-specific properties to be specified.

Free energy plugin added
Plugin will not run w/ Obc or GB/VI forces unless line 2004 of gpu.cpp (gpu->sim.totalNonbondOutputBuffers  = 2*gpu->sim.nonbondOutputBuffers;) is commented in -- working on removing this constraint
Also unit tests for GB/VI currently fail 

Restructured how force and energy computations are done to make it easier to write plugins for the CUDA platform