Fix typo in comment
uncrustify
Fix tree freeing

We need to look at all allocated nodes, not just the ones reachable from the
tree. Some nodes may be removed from the tree but still have SVs that need
their reference count decremented.

Also, make sure that the SV is SvOK before decrementing. It's possible for two
nodes to end up sharing the same key SV (at least, I think that's what is
happening).