Fix failing TOC specs, update next_chapter_link for guides/index.html

I was trying to make a separate pull request for some stuff I was testing out using the toc.rb file and I noticed the specs were failing. A few were failing because content has since been rearranged, so I simply updated the specs to reflect that. There was also a spec about showing "WARNING: EMBER-DATA IS A WORK IN PROGRESS AND UNDER RAPID DEVELOPMENT. USE WITH CAUTION!!!", but that has since been removed from the models guide, so I simply removed that spec.

The only gotcha I noticed was that when you visit /guides (which is /guides/index.html), you see as the 'next' link as: 
![We're done with Ember.js Guides. Next up: Getting Started - Getting Started →](https://f.cloud.github.com/assets/2406167/1651270/0b7b1e94-5acd-11e3-9b4f-476ff41e5a0e.png)

Based on what I could infer from the tests (the fact that it does not share the "Shows next section link" example that checks for "We're done with"), I figured that it would probably be better to update the code to just show 'Getting Started'. This updated branch:

![screen shot 2013-12-01 at 3 13 02 pm](https://f.cloud.github.com/assets/2406167/1651280/6069c658-5acd-11e3-9836-7aa89eb8663b.png)

Just check next_chapter_link and if the section_slug is index.html (a pattern repeated elsewhere in toc.rb), only show the title. 

Now all specs pass!