[FIX] point_of_sale: set taxes when creating pos_order from form view

When creating pos_orders from the form view, tax_ids on the
pos_order_lines were never set.

This was kind of fixed in 5327869356. But
in there it was in onchange_qty, because the way the fiscal position was
taken into account required it to be. Because we take the fiscal
position into account in a different way now we can assign the taxes in
onchange_product_id which makes a bit more sense.

addons/point_of_sale/point_of_sale.py

@@ -1403,6 +1403,10 @@ class pos_order_line(osv.osv):
 
         result = self.onchange_qty(cr, uid, ids, pricelist, product_id, 0.0, qty, price, context=context)
         result['value']['price_unit'] = price
+
+        prod = self.pool.get('product.product').browse(cr, uid, product_id, context=context)
+        result['value']['tax_ids'] = prod.taxes_id.ids
+
         return result
 
     def onchange_qty(self, cr, uid, ids, pricelist, product, discount, qty, price_unit, context=None):

addons/point_of_sale/point_of_sale_view.xml

@@ -51,6 +51,7 @@
                                         <field name="price_unit" on_change="onchange_qty(parent.pricelist_id,product_id, discount, qty, price_unit, context)" widget="monetary"/>
                                         <field name="price_subtotal" invisible="1" widget="monetary"/>
                                         <field name="price_subtotal_incl" invisible="1" widget="monetary"/>
+                                        <field name="tax_ids" widget="many2many_tags"/>
                                         <field name="notice"/>
                                     </group>
                                 </form>