Update FormField.php

Allows the label to be highlighted as well when adding a class of has-error or has-success to the containing form-group div as seen in the TWBS3 docs.

http://getbootstrap.com/css/#forms-validation

![image](https://f.cloud.github.com/assets/1517011/1927872/0529e846-7e6c-11e3-91d6-cd780f9ddb96.png)