sort/group by a field that's NOT the title

Example case: A contact list that's titled with a persons fullname, but I want the alpha paging to operate on the lastname (a separate CCK textfield).

A similar case is indexing on scientific name vs common name for plants/genus indexes

Currently, when the code chooses the primary grouping field ($sortfield) it just iterates and looks for the first instance of 'sortable'.

When (in a table view) I still want the title/fullname to be the first displayed column, but the lastname to be the one indexed, this doesn't work. Unless I disable sorting on title altogether (which is a reasonable option too)

However, it looks to make a little bit more sense to choose the field that's set as 'defaultsort' in the view definition. The unique 'defaultsort' setting is more explicit than the multiple 'sortable' and the fallback behaviour will continue to be the same out-of-the-box.

before:

    foreach ($view->field as $field) {
      if (!empty($field['sortable'])) {
        $sort_field = $field['fullname'];
        break;
      }
    }

after:

    foreach ($view->field as $field) {
      if (!empty($field['defaultsort'])) {
        $sort_field = $field['fullname'];
        break;
      }
    }

Does this sound reasonable?