Don't underline navbar links on hover; instead give it a mid-grey bottom border.

r? @spasovski @ngokevin

![screen shot 2014-08-21 at 6 42 34 pm](https://cloud.githubusercontent.com/assets/23885/4005601/4f232172-2995-11e4-93a1-2945b3b33b9a.png)

"New" is active, "Popular" is hover.
whitespace