message: Made stl_emulation.h usable by itself.
diff: #include <string>
  #include <type_traits>
  #include <vector>
  +#include <memory>
  +#include <limits>
  #if defined(_STLPORT_VERSION) && !defined(FLATBUFFERS_CPP98_STL)
  #define FLATBUFFERS_CPP98_STL
  