Fix issue using Collapse without Panel

[zessx]

Overview

If you try to use Collapse without Panel, you must use the .panel class to get it work.

Example

<div id="accordion">
  <div>
    <a data-toggle="collapse" data-parent="#accordion" href="#collapseOne">Item #1</a>
    <div id="collapseOne" class="collapse in">
      Lorem Ipsum
    </div>
  </div>
  <div>
    <a data-toggle="collapse" data-parent="#accordion" href="#collapseTwo">Item #2</a>
    <div id="collapseTwo" class="collapse">
      Lorem Ipsum
    </div>
  </div>
  <div>
    <a data-toggle="collapse" data-parent="#accordion" href="#collapseThree">Item #3</a>
    <div id="collapseThree" class="collapse">
      Lorem Ipsum
    </div>
  </div>
</div>

Expected behavior

On Item #2 click, we expect the first block (under Item #1) to collapse, and the second one (under Item #2) to extend.

Current behavior

On Item #2 click, and the second block (under Item #2) extends. The first block (under Item #1) doesn't collapse.

[cvrebert]

Duplicate of #10966.
This particular change rejected per #10966 (comment)