Explore dropdown menu is hidden behind other resources in IE

- View a dataset with multiple resources in IE7 e.g. http://master.ckan.org/dataset/adur_district_spending
- Click on explore button of top resource
- The menu is hidden behind the resource below (see screenshot)

![ie7 clean running](https://f.cloud.github.com/assets/199920/536841/75b78ece-c161-11e2-8079-3021e11d5f52.png)