[FIX] purchase: date planned

When a PO is copied, the date planned of the order lines should be
recomputed based on the order date.

opw-675480

addons/purchase/purchase.py

@@ -186,6 +186,16 @@ class PurchaseOrder(models.Model):
                 raise UserError(_('In order to delete a purchase order, you must cancel it first.'))
         return super(PurchaseOrder, self).unlink()
 
+    @api.multi
+    def copy(self, default=None):
+        new_po = super(PurchaseOrder, self).copy()
+        for line in new_po.order_line:
+            seller = line.product_id._select_seller(
+                line.product_id, partner_id=line.partner_id, quantity=line.product_qty,
+                date=line.order_id.date_order and line.order_id.date_order[:10], uom_id=line.product_uom)
+            line.date_planned = line._get_date_planned(seller)
+        return new_po
+
     @api.multi
     def _track_subtype(self, init_values):
         self.ensure_one()