Treat numeric node names with leading zeroes as different from those wit...

...hout. -- #234

(Note that I looked into adding a unit test for this but couldn't find a way to easily test this portion of `Node::addNode` without adding a lot of extra code.)
In my experience as a user, even when I add a numerically-named node, it is converted to a string somewhere along the way. However, I do not know the code intimately enough to guarantee that this is always the case, it was only what I observed.