[FIX] sale, purchase: currency in subtotal

The "Subtotal" field of a SO/PO line is not rounding following the
currency rules.

opw-710701

addons/purchase/views/purchase_views.xml

@@ -210,6 +210,7 @@
                         <page string="Products">
                             <field name="order_line" attrs="{'readonly': [('state', 'in', ('done', 'cancel'))]}">
                                  <tree string="Purchase Order Lines" editable="bottom">
+                                    <field name="currency_id" invisible="1"/>
                                     <field name="state" invisible="1"/>
                                     <field name="sequence" widget="handle"/>
                                     <field name="product_id" attrs="{'readonly': [('state', 'in', ('purchase', 'to approve','done', 'cancel'))]}" context="{'partner_id':parent.partner_id, 'quantity':product_qty,'uom':product_uom, 'company_id': parent.company_id}"/>

addons/sale/views/sale_views.xml

@@ -289,6 +289,7 @@
                                     <field name="state" invisible="1"/>
                                     <field name="invoice_status" invisible="1"/>
                                     <field name="customer_lead" invisible="1"/>
+                                    <field name="currency_id" invisible="1"/>
                                 </tree>
                                 <kanban class="o_kanban_mobile">
                                     <field name="product_id"/>