Added destroyfailed event

Added possibility to inform user about failed deletes.

to be used with:
$('#fileupload').on('fileuploaddestroyfailed', function (e, data) {/* ... */})
Merge pull request #2859 from jbirkholz/master

Added destroyfailed event
Updated version number.
Merge branch 'master' of https://github.com/blueimp/jQuery-File-Upload