[FIX] orm: set default before removing magic fields

When a record is created, the magic fields (id, create_date,...) are first removed from the vals as the user should not set a value for these.
However if a value for this is given in default value (e.g. defined in an ir.value), the creation would crash (sql error : column specified more than once) as the magic column would be added again.
[FIX] product_visible_discount: multicurrency pricelists

When we compute the discount of a product to display (result of product_id_change), we compare prices in the currency of the product while we expect prices in the currency of the pricelist. opw 606188