VS2013 compile errors

I pulled the `master` branch from github and used the latest CMake, SWIG, and Microsoft's current free compiler (Visual Studio 2013 Express for Desktop) to build.

There were a few compiler errors, mostly stemming from VS2013 conforming better to C++ standards.

The only change which I'm not happy about is the last -- defines for serialization_files that are specified in CMakeLists.txt ( https://github.com/SimTk/openmm/blob/230819d1e7340f320666c47a8cd3c4f396406ffb/CMakeLists.txt#L433  ) are not communicated to visual studio.  As a workaround I have added #defines for them directly in the source files.  I will try to figure out why CMake isn't generating the right thing, and if I can, will amend the PR to do it correctly.