CRM-16481 - Apply discounts if any; line_item is updated

CRM-16481 - Apply discounts if any; line_item is updated

Because multiple events are processed and the form isn't modeled on registerEvent, it was necessary to manually invoke discount methods; normally the hook buildAmount would do it - perhaps it'd be better to rewrite this page using buildAmount.
note: Line_item update has been added in this version's post_process already
Conflicts:
	CRM/Event/Cart/Form/Checkout/Payment.php