Follow up 5ce8055
* Changed wrong flag value, 6 -> 4
* Added UID check in pc_cart_additem()
* Generate GUID moved to pc_additem() for item with flag.guid
* Added card comparison in 'mergeitem' to avoid merge CARD0_* items with non-CARD0_*

Signed-off-by: Cydh Ramdh <house.bad@gmail.com>