A method for checking if an object is an intermediate object between root and leaf?

I have a multi-level tag hierarchy and I happened to need to know if a tag is a parent of sub-tags, but not a root. I ended up adding this to the Tag model:

```
def intermediate?
  !self.root? && !self.leaf?
end
```

I think that something similar would be a good idea as an instance method in the gem.
