fix bug 845233 - Adding TOC line indent

You win this round, Orchard....

https://bugzilla.mozilla.org/show_bug.cgi?id=845496

Use this text to test:

```html
<h2>Heading 2</h2>
<p>&nbsp;</p>

<h3>Heading 3</h3>
<p>&nbsp;</p>

<h4>Heading 4</h4>
<p>&nbsp;</p>

<h2>Heading 2 (that is way longer than it should be)</h2>
<p>&nbsp;</p>

<h3>Heading 3 (that is way longer than it should be)</h3>
<p>&nbsp;</p>

<h4>Heading 4 (that is way longer than it should be)</h4>
<p>&nbsp;</p>

<h2>Heading 2</h2>
<p>&nbsp;</p>

<h3>Heading 3</h3>
<p>&nbsp;</p>

<h4>Heading 4</h4>
<p>&nbsp;</p>
```