Fix iframe fallback when the message is sent from a popup in IE

In Internet Explorer an "Operation Aborted" error will throw when an opened window is trying to call a function on a parent which this one will do a `postMessage` (the error is silent due to the `catch (x) {}`).

Requeuing the `postMessage` at the end of the execution queue with a `setTimeout(0)` fix the problem ([source](http://stackoverflow.com/questions/9703730/does-html5-support-cross-window-messaging#comment18932554_9706518)).