Change Hierarchical List to be rooted at a task instead of at a vector

[GoogleCodeExporter]

At the beginning I made a bad decision to store top level tasks in a vector, 
but all subtasks go inside parent tasks.  This has required separate 
functions for root tasks and all other tasks.  Allowing the list view to be 
rooted at a root Node instead of a root Vector will simplify everything, and 
allow us to fix other issues such as issue 1.

Original issue reported on code.google.com by [email protected] on 15 Jul 2009 at 1:46

[stweise]

Hey @gtaubman do you have any thoughts on this? Could you please look at the PR?

[stweise]

The proposed changes introduced a lot of other issues. I could not solve this correctly and I still think that representing the initial list of listroots, which are then hierarchical lists is not a bad decision in terms of matching model to code.