[FIX] purchase: supplier taxes in onchange_product_id

When adding a line in a PO with the SUPERUSER_ID all the record rules
didn't apply on him. Then all the supplier taxes set on the  product
were written in the PO line even if some of its were not in the company
of the user. Then with the SUPERUSER_ID, just the company taxes of this
user must be applied. Inspired from product_id_change in model
'sale.order.line'.

opw:659236

addons/purchase/purchase.py

@@ -1253,7 +1253,11 @@ class purchase_order_line(osv.osv):
             else:
                 price = product.standard_price
 
-        taxes = account_tax.browse(cr, uid, map(lambda x: x.id, product.supplier_taxes_id))
+        if uid == SUPERUSER_ID:
+            company_id = self.pool['res.users'].browse(cr, uid, [uid]).company_id.id
+            taxes = product.supplier_taxes_id.filtered(lambda r: r.company_id.id == company_id)
+        else:
+            taxes = product.supplier_taxes_id
         fpos = fiscal_position_id and account_fiscal_position.browse(cr, uid, fiscal_position_id, context=context) or False
         taxes_ids = account_fiscal_position.map_tax(cr, uid, fpos, taxes)
         price = self.pool['account.tax']._fix_tax_included_price(cr, uid, price, product.supplier_taxes_id, taxes_ids)