blueimp/jQuery-File-Upload — pull request #1939 by mdornseif (2012-12-16 12:35:36+00:00)
Title: Helps to upload files in the order they appear in the UI.

Also keeps parallel requests to the server at bay thus saving server resources.
The approach taken here is not 100 percent reliable but reduces
out of order uploads a lot.

See also https://groups.google.com/forum/#!searchin/jquery-fileupload/appengine/jquery-fileupload/osntyW7yDLg/jRtduHTHw6UJ

I'm not sure if 500 ms delay per upload is the right time - maybe this should be configurable?
I'm seeing the out of order upload behaviour with a `submit` AJAX hook on AppEngine - so this might be the reason I see out of order uploads.

Whatever I think wiring the click() events not to fast is a good thing.