PayPalPro.module: Express checkout HTML typo and product_adjust_price call rather than just get price

Two minor tweaks to Jermey's great new module... There is an end-HTML tag that should be end-HEAD in paypalpro_express_checkout_redirect, and more importantly, there is a need to get the item pricing through product_adjust_price rather than an attribute-get in paypalpro_doExpressCheckoutPayment.

This is a super module... thanks, Jeremy!