Visual Studio Ultimate 2013 Update 2 RC optimized builds

When compiling using Visual C++ with optimization (such as `Maximize Speed (/O2)`), the compiler produces bad code in regards to the `Score` object. If you run the resulting code without `NDEBUG`, `bench` asserts an out-of-bounds `Score`:

> Position: 1/30
> Assertion failed: -VALUE_INFINITE < mg_value(v) && mg_value(v) < VALUE_INFINITE, file ..\..\repos\stockfish\src\evaluate.cpp, line 230
 
This may be related to this [bug in the Visual C++ compiler 64-bit code generator](http://info.prelert.com/blog/visual-cpp-code-generation-bug).

This patch fixes that.