Updated Tree specs to account for unordered criteria results
Merge branch 'master' into feature-has-ancestry
Added custom #children relation to HasAncestry concern

- Current spec status: 113 examples, 0 failures, 1 pending.
- TODO count: 5.
Added specific error subclasses for HasAncestry errors; added specs

- Current spec status: 115 examples, 0 failures, 1 pending.
- TODO count: 0.