Implement deleted_conflicts

RevisionTreeIndex.php contains the todo

  /**
   * Recursive helper method to build the revision tree.
   *
   * @return array
   *   Returns an array containing the built tree, open revisions, default
   *   revision, default branch and conflicts.
   *
   * @todo Implement 'deleted_conflicts'
   */
  protected static function doBuildTree($revs, $revs_info, $parse = 0, &$tree = array(), &$open_revs = array(), &$conflicts = array()) {