rem: bplustree_header::CheckNode(bplustree_node *node)
add: bplustree_header::CheckNode(bplustree_node *node) const
context: bplustree_header::CheckNode(bplustree_node *node){	// sanity checks (links, all_key_count)	return IsValidLink(node->LeftLink())		&& IsValidLink(node->RightLink())		&& IsValidLink(node->OverflowLink())		&& (int8 *)node->Values() + node->NumKeys() * sizeof(off_t) <= (int8 *)node + NodeSize();}