[FIX] sale_margin: margin handle included taxes for sale

Another fix should probably be build for purchase price, but it isn't that easy, we need to know the partner to which the product has been purchased, as taxes are partner/country dependent.

Besides, included taxes in purchase prices happen less often.

addons/sale_margin/sale_margin.py

@@ -52,10 +52,7 @@ def _product_margin(self, cr, uid, ids, field_name, arg, context=None):
         for line in self.browse(cr, uid, ids, context=context):
             res[line.id] = 0
             if line.product_id:
-                if line.purchase_price:
-                    res[line.id] = round((line.price_unit*line.product_uos_qty*(100.0-line.discount)/100.0) -(line.purchase_price*line.product_uos_qty), 2)
-                else:
-                    res[line.id] = round((line.price_unit*line.product_uos_qty*(100.0-line.discount)/100.0) -(line.product_id.standard_price*line.product_uos_qty), 2)
+                res[line.id] = round(line.price_subtotal - ((line.purchase_price or line.product_id.standard_price) * line.product_uos_qty), 2)
         return res
 
     _columns = {