Script to track Ajax requests on a page to determine when it's done loading. Provides a function to the global namespace, callWhenReadyToGo, that takes a callback function which is called when the window has loaded and there are no pending Ajax requests.
Doesn't always work when the page involves requests made via some higher-level libraries. In general, if the request is performed using the XMLHttpRequest API and concludes (successfully or not) with an onreadystatechange event changing the readyState value of the XHR request to the value of XMLHttpRequest.DONE the tracker understands the XHR request to no longer be pending. If onreadystatechange is not fired, or readyState is not ultimately set to the value of XMLHttpRequest.DONE the tracker will indefinitely consider the request to be pending, so will not consider the page to have ever loaded.