Minimum contribution amount check for Premiums fails when online contribution form uses a Membership price set.

Basically the code which checks whether total amount is sufficient for selected premiums doesn't work for membership price sets.

Recreated this on my local 4.4 site as follows:

• Create new prices set - type = Membership
• Add a radio button field and populate w/ the 2 sample membership types (General & Student)
• Modify the existing sample contribution page id=2 to use the new price set
• Add the Coffee Mug premium to that page

Even though either membership type selected has total_amount > $5 minimum for the Mug, you get the error: "You must contribute at least $ 5.00 to get this item" when you try and select the Mug. Switch the page back to using quick-config (i.e. deselect the price set and enable the 2 membership type checkboxes) and it works properly.