Use more specific CSS selector to allow for embedding in fuelux containe...

Hi Marijn,

If you embed codemirror on a fuelux or bootstrap container, I get the effect below (firefox 30.0 on Ubuntu).
This pull request makes the CSS of CodeMirror `pre` elements a bit more specific to make it overrule.  See
image below.

    Thanks for CodeMirror

       --- Jan

![cm-fuelux](https://cloud.githubusercontent.com/assets/3071146/3598746/21201ca0-0ce7-11e4-82aa-a5766c9446d6.png)