Secondary filters don't display Title and Description

This is sort of related to #2019871: Label for "is between" secondary filters missing, but not exactly.

When a filter is made into a "Secondary option", the title and description of that option fail to render. In the code that copies the filter into the $secondary array, the title is copied over (though not the description), but since $secondary[$identifier] doesn't have a type of it's own, it is rendered as a "markup" form element which does not accept #title or #description as a property (see documentation).

The way the code is now, the BEF filter looks roughly like (warning, psuedo-array!):

array(
  '#title' => 'BEF label',
  'min' => array(
    '#title' => '',
    // ...
  ),
  'max' => array(
    '#title' => 'And',
  ),
  '#bef_description' => 'Some descriptive text.',
)

I have attached a patch which adds $secondary[$identifier]['#type'] = 'item';, and it copies the description from '#bef_description' (or $form['#info'][$filter_key]['description'] as a fallback).

That brings up one more question... why is there a description in the BEF options form when the filter form has it's own description field? Seems sort of redundant to me, but I'd like to hear the reasoning behind it.