Fix syntax highlighting

Don't break highlighting on multi-line spans (multi-line comments for
example).  

See #6546

Before:

![screen shot 2014-04-22 at 5 06 41 pm](https://cloud.githubusercontent.com/assets/677994/2771412/9a2ef0e0-ca6a-11e3-9f5a-c99c19a880fc.png)

After:

![screen shot 2014-04-22 at 5 02 17 pm](https://cloud.githubusercontent.com/assets/677994/2771415/a2b40b7e-ca6a-11e3-9fbe-efab8513b719.png)