GitLab

- MingW, where "WIN32" is set by CMake but the compiler is not Microsoft's (should use _MSC_VER) in that case, and 
- in gcc 4.4 which is fussy about some issues that earlier versions were silent about, such as passing a string constant to a "char*" rather than a "const char*".
I also fixed a syntax error in CMakeLists that showed up in the OpenMM workshop for some unknown reason.

Brook is not currently building correctly; I think it has not yet been fully converted to the getTime() interface needed for variable step integrators.

In calcForces() kReduceBornSumAndForces kernel is not needed since Born radii/Obc chain term now calculated prior to calculation of forces
Modified kCalculateObcGbsaBornSum kernel loop to match that in kCalculateCDLJObcGbsaForces1; Born sums are zero w/o mods

Optimization to constraint algorithm: skip the last iteration as soon as we see that all constraints have converged.

License header changes; force duplication factor to 4; fixed potential problem w/ Shake -- if no constraints, pgm crashes

Eliminate some VC++ build problems via the usual expedient of explicit casts from unsigned to signed and from double to float. TNT Arrays apparently can't be indexed with unsigned because VC++ finds something ambiguous then above their operator[] methods.

Added Platform::getDefaultPluginDirectory().  Plugins are now installed into .../openmm/lib/plugins.