Fixed autocomplete not showing in fullscreen mode

Autocomplete was being hidden because of the z-index on the Fullscreen class. I added a z-index to .CodeMirror-hints just a smidgeon higher than editor so it can overlay properly.

![Fullscreen Autocomplete In Action](https://f.cloud.github.com/assets/137686/1990513/b57c3446-8485-11e3-94bb-86142cf5773b.png)