the type writing more explictly tied to the size type, with use of unsigned int as the default size. This approach
ensures that we get the same results under 32 and 64bit builds.
From Robert Osfield, refactor of Wang Rui's original osg2 into 3 parts - parts placed into osgDB, the ReaderWriter placed into src/osg/Plugin/osg and wrappers into src/osgWrappers/serializers/osg