fix Safari drag&drop functionality when cancelling dragover event in parent element

[gonchuki]

At least on Safari Windows, if you cancel the dragover event on any parent element of the droppable area (to prevent the browser from opening a file that was dropped outside of our designated area), then Safari completely ignores the drop action. (nothing happens at all)

This patch has been on our production code for at least 4 months so I would say it's quite safe for merging. Not sure if anyone should actually depend on this event bubbling up on the DOM, we don't use the built-in queue plugin so let me know if this patch is no good.

[j-manu]

How did you actually cancel the event? I tried capturing the event and calling preventDefault, by adding a listener to "body" but the browser (FF) opens the image if it is dropped outside the drop zone. The event on body does not seem to fire.
Since the user can drop the file anywhere, body seemed the only logical place to trap all drops but it is not working out :(

[gonchuki]

if (document.body.addEventListener) {
  document.body.addEventListener('dragover', function (e) { if (e.dataTransfer && (Array.prototype.indexOf.call(e.dataTransfer.types, 'Files') !== -1)) e.dataTransfer.dropEffect = 'none'; e.preventDefault(); }, false);
  document.body.addEventListener('drop', function (e) { e.preventDefault(); }, false);
}

short explanation:

• you need to prevent both drop and dragover for this to work
• you only want to prevent users from dropping files, dragging and dropping text into forms should still be accepted, thus that's why I check on e.dataTransfer
• the drop effect thing changes the cursor to the "forbidden" one.

[NeoXidizer]

gonchuki, thank you very much for this fix!
P.S. this code also breaks the latest safari on Windows

$('#dropZone').bind('dragover', function(e){
    $(this).addClass('hover');return 0;
});

[jayarjo]

In Plupload 2 we've now removed the whole fakeSafariDragDrop thing.