(this is the same constant value for all properties)
else if(!strcmp(a, "references")) return naNum(node->getNumRefs());
else if(!strcmp(a, "tied")) return naNum((*node)->isTied());
else if(!strcmp(a, "alias")) return naNum((*node)->isAlias());
+ else if(!strcmp(a, "last")) return naNum(SGPropertyNode::LAST_USED_ATTRIBUTE);
else if(!strcmp(a, "readable")) attr = SGPropertyNode::READ;
else if(!strcmp(a, "writable")) attr = SGPropertyNode::WRITE;
else if(!strcmp(a, "archive")) attr = SGPropertyNode::ARCHIVE;