Handling a TraversedPartialPath exception is awkward

[carver]

What was wrong?

In an older HexaryTrieFog API, the TraversedPartialPath exception arguments made more sense. Now, they don't really help you use the fog API without a lot of argument fiddling.

What did you expect it to do?

TPP can return a "simulated" node which helps cleanly deal with the case of using the fog to traverse to a path that doesn't exist anymore.