fix raised-linked toolbar button borders

After installing Rhythmbox3 found this issue with raised linked toolbar buttons:
![linked_button_issue](https://f.cloud.github.com/assets/2231759/1376163/02b0a1ce-3a90-11e3-92d9-4d34c944d8dd.png)

This pull request fixes the problem:
![fixed_borders](https://f.cloud.github.com/assets/2231759/1376187/52042b88-3a90-11e3-91a3-1d8ddd123d93.png)

This is my first pull request so hopefully it is done properly.