Adds support for step titles nested in contents

I'm using formtastic in a Rails app, and wanted to add jquery.steps to one of my forms, but i found some difficulties since this forces forms to have the following structure:

```html
<form>
  <titleTag>Title 1</titleTag>
  <bodyTag>Content 1</bodyTag>

  <titleTag>Title 2</titleTag>
  <bodyTag>Content 2</bodyTag>
</form>
```

while I usually prefer a more structured option, pretty much like the default one that formtastic does for me on this specific case:

```html
<form>
  <bodyTag>
    <titleTag>Title 1</titleTag>
    Content 1
  </bodyTag>

  <bodyTag>
    <titleTag>Title 2</titleTag>
    Content 2
  </bodyTag>
</form>
```

The only thing preventing jquery.steps from handling this was because it was using `children()` to find all titles and bodies. Switching to the `find` method allowed to use nested selectors such as this:

```javascript
$('#new_user').steps({
  'headerTag': 'fieldset legend',
  'bodyTag': 'fieldset'
});

and everything else seems to work fine.
I just didn't know how to go about the test suite, since i have 0 experience with QUnit. My (stupid) approach was to just duplicate the original tests, but this time isung a form with the newly supported structure
There's got to be a better way to test this though...