arithmetic product operations in tree views

[Numérigraphe]

Wishlist: have a new attribute in tree views to get the arithmetic product of values displayed on the bottom of the view.
Example:
                    <field name="advance_percent" multiply="Total advance (%)" />

[Numérigraphe (numerigraphe)]

Please note that this take all the records in the domain, and not take the limit into account (80 rows only by default on the GTK client).