Remove display: run-in from thread indicators

This is broken in Safari and removing it doesn't appear to affect the rendering in any of the other browsers.

![screen shot 2014-08-25 at 15 47 57](https://cloud.githubusercontent.com/assets/47144/4030579/75b9e890-2c5e-11e4-8440-1b487071ba0b.png)

Note the run-in acts as `display: block` in Safari.