Bad integration in field_group vertical tab

Wrong integration : 
![wrong](https://cloud.githubusercontent.com/assets/1424035/3200662/f716dc6e-ed7e-11e3-9c26-afc7be9f20ca.PNG)
you can see fields are split into multiple lines which is awful

<hr/>

After patch application : 
![good](https://cloud.githubusercontent.com/assets/1424035/3200669/08ada8fe-ed7f-11e3-816e-785babc07053.PNG)
fields are correctly aligned