[IMP] product: get_history_price multi to ease migration

This method is used only in stock_account that is about to be migrated
into the new API. To ease the migration the method is converted into
a multi method, using a decorator.

addons/product/product.py

@@ -1218,6 +1218,7 @@ class product_product(osv.osv):
             'company_id': company_id,
         }, context=context)
 
+    @api.cr_uid_ids_context
     def get_history_price(self, cr, uid, product_id, company_id, date=None, context=None):
         if context is None:
             context = {}

addons/stock_account/wizard/stock_valuation_history.py

@@ -97,7 +97,7 @@ class stock_history(osv.osv):
             if line.product_id.cost_method == 'real':
                 res[line.id] = line.quantity * line.price_unit_on_quant
             else:
-                res[line.id] = line.quantity * product_obj.get_history_price(cr, uid, line.product_id.id, line.company_id.id, date=date, context=context)
+                res[line.id] = line.quantity * product_obj.get_history_price(cr, uid, [line.product_id.id], line.company_id.id, date=date, context=context)
         return res
 
     _columns = {