You can add a package twice to a group

[jwyg]

To reproduce (from Jonathan Gray):

• I go to add an item to the group
• As I type, I get autocomplete options (cool!)
• When I click on one, it adds this, and copies the same autocomplete option in the box
• When I click submit, it seems to add the item twice
• On the main group page I think it just shows up once, but when I click edit it shows two identical boxes, both ticked - and the count includes two copies of the same item

Basically the problem is allowing the same package associated multiple times with a group.

This is an issue on CKAN 1.5b and probably earlier.