fixed time picker arrows box-shadow when active

before

![before](https://cloud.githubusercontent.com/assets/677646/4065347/ce76c6f8-2e19-11e4-9b1d-1e4f5c144ea1.png)

after

![after](https://cloud.githubusercontent.com/assets/677646/4065351/d69ed370-2e19-11e4-9a44-271a9c3eb2d8.png)

(note the box shadow for the pressed arrow)