acts_as_tree

Hi folks,

For my app, I needed to modify acts_as_tree (ActiveRecord::Acts::Tree)
such that deleting a node would orphan sub-nodes, rather than deleting
them. This is accomplished simply by allowing a :dependent option to
the acts_as_tree method so that it can be set to :nullify. For my app,
I simply did this by adding a file tree.rb to my lib directory and
requiring it in the model.

A number of unit-test later it seems like this works fine re all the
instance methods (ancestors, siblings, self_and_siblings, roots). So,
I'd like to submit a patch via Trac with this small change, but since
this would be my first, I thought I'd check in here before doing so to
see if there is any reason why I shouldn't, or if I should use a
different approach.

Thoughts?

-Eric