Html5 DnD may remain stuck under WebKit when there are multiple big files

Under WebKit the load can not be used because it may be filed a little bit too early (load is completed on the client side but not the server side).

The current DnD code does a workaround using 2 tricks :

• use progress event : 100% => means completed
• track state change

When files are big, the last progress event may be 99.9999% but there is usually no notfication on progress for completion.

This means we have to rely on "state change".

However, there is currently a closure issue in the way the onreadystatechange callback is defined.

Initial code : the closure on xhr is not done correctly

 xhr.onreadystatechange = function() {readyStateChange(xhr, opts)}

Modified code : force closure to be sure the call backs will contain the correct values

xhr.onreadystatechange = (function(xhr,opts) { return function() {readyStateChange(xhr, opts)}})(xhr,opts);

NB : JavaScript is such a nice language ...