From Lilin Xiong, "When writing proxyNode to ive file, we forget "LoadingExternalReferenceMode ". Add some code to fix this.

if (out->getVersion() >= VERSION_0045)
{
    out->writeInt(getLoadingExternalReferenceMode());
}

if (in->getVersion() >= VERSION_0045)
{
   setLoadExternalReferenceFiles( (osg::ProxyNode::LoadingExternalReferenceMode)in->readInt() );
}
"