dragenter needs to be preventDefault'd too
dragenter needs to be preventDefault'd too

The default action of dragenter is to "Reject immediate user selection as
potential target element". Internet Explorer follows this, and therefore
stops the drag and drop from working as intended.

See http://www.w3.org/html/wg/drafts/html/master/editing.html#dndevents
and
http://www.quirksmode.org/blog/archives/2009/09/the_html5_drag.html

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