File Drop: Handle file upload drag and drop operations

This object can handle file upload drag and drop operations.

It can setup page elements to handle file drag and drop operations in a way that works independently of the browser. It works in Firefox 3.6, Internet Explorer 6, Google Chrome 7, SRWare Iron 4, Apple Safari 5 and Opera 11.61.

It uses the File API if the browser supports it or users iframes otherwise.

Files can be uploaded using AJAX requests when dropped in the target elements.

Callback functions may be called when certain events occur like when the mouse pointer enters or leaves a drop target element while dragging a file, a file is dropped, the upload is started, upload progress, the upload is done, etc..