biocore/scikit-bio — pull request #309 by wdwvt1 (2014-05-08 03:18:26+00:00)
Title: Tree method addition

This adds the functionality of cogents ```totalDescendingBranchlength()``` method to skbio ```TreeNode```.

There are two components of the code that I am unsure about.
First is the copying of the tree that occurs on line 2536. I didn't want to propagate my own attribute through self so I copied the tree. Is there a superior way to do this?
Second, I am moving through the tree several times. For instance, I move through to remove the internal node names to avoid a ```DuplicateNodeError```. I could wrap this in to another one of the traversals but unsure if necessary.

Thanks to @wasade for the main logic of this function.