fix calendar view record read error when event_open_popup is set


![qq20141006-2](https://cloud.githubusercontent.com/assets/1754190/4526750/3d21eb34-4d62-11e4-9682-86eb4c04003f.png)
event.id is a type of integer ,and event._id is the string version of event.id.
in most models(exclude calendar.event),read method does not accept ids to be string type,so it report an error,but the event_open_popup parameter of calendar view was only being used in calendar  module for calendar.event ,so  this bug has never been found before.