Work on a copy of the headers in _initXHRData
Work on a copy of the headers in _initXHRData

If someone passes a "headers" options to fileupload(), this object get overwritten across multiple files upload because the same object is being re-used.
blueimp/jQuery-File-Upload,Verde1705/verde1705.github.io,blueimp/jQuery-File-Upload,blueimp/jQuery-File-Upload,blueimp/jQuery-File-Upload,Verde1705/verde1705.github.io,blueimp/jQuery-File-Upload,blueimp/jQuery-File-Upload