Add a `getTree()` method to `AASTNode`
Add a `getTree()` method to `AASTNode`

Summary: Basically, I want to use `AASTNodeList::newFromTreeAndNodes`, but don't have access to the tree.

Test Plan: N/A

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D11781

julkiewicz/libphutil,julkiewicz/libphutil,julkiewicz/libphutil