renewal link disappears when product is in cart

When someone clicks on the 'renew' link on the 'store/subscriptions' page, but then doesn't immediately go through with the purchase, the product remains in the users cart, and this means that the 'renew' link (correctly I guess) disappears. Unfortunately the 'this product is already in your cart' text, which is generated, is not actually used. The patch I've attached preserves the 'renew' link when the product is already in the cart, but takes the user through to the cart page instead of the the renewal page if it's already in the cart (this was the most compact way I could come up with of indicating this - perhaps the user doesn't need to be told the product is in the cart anyway). I haven't got rid of the superfluous 'this is in your cart' text 2 lines before the patch but iperhaps whoever applies the patch could get rid of that too if they feel it's unneeded.