Javascript error when adding a dataset in IE7

Tested on Master in IE7. (http://master.ckan.org/dataset/new - running 956a1b6)

When you choose any of the drop down menus (e.g. Licence) on the add dataset page you get a JS error. 

See screenshot

![ie7 clean running](https://f.cloud.github.com/assets/199920/590477/cfca4eda-c9e3-11e2-8782-a84b4571b3ab.png)