Removed Quick Open dropdown menu border and tweaked its dropshadow to compensate

This is for #7307. 

![screen shot 2014-03-24 at 3 55 30 pm](https://f.cloud.github.com/assets/1495261/2506497/de37bc2e-b3a7-11e3-98e3-136fbde3f2c6.png)