pinHeader userbar floats not-at-top on subreddits which customize userbar position

![screen shot 2014-06-19 at 7 27 59 pm](https://cloud.githubusercontent.com/assets/455632/3335324/d0c7d318-f811-11e3-80ed-77d207c74cbc.png)
e.g. /r/Theoryofreddit