Pickling an Element object works correctly
Merge branch 'master' of https://github.com/peastman/openmm
RPMD works correctly with a barostat
Fixes for compilation errors on Visual Studio 2013
Plugins work with CPU platform.  This involved separating the reference implementations of plugins into their own libraries.
All code is compiled with SSE enabled.  This eliminates errors with some compilers.
Reference implementation of AndersenThermostat did not handle massless particles correctly
Merged latest changes from main branch
Minor fix to Python wrappers