Blender Git Loki

OCIO: Disable the warnings related on C4251

Those warnings are trigerred by stl classes in OCIO's public interface.

To quote MSDN: "C4251 can be ignored if you are deriving from a type in
the Standard C++ Library"

This is the only instance where those warnings hunts us, so for now we
can keep it all local in intern/opencolorio but this might be changed
in the future.