SWC-639: fix upload for IE (for now limit to 5mb)

fixed multiple issues with IE upload. Chunked upload caused Network Error 0x2efe (SWC-639).  File name from windows box included full path, so there was always an error on rename.  And json response is automatically unwrapped in some cases, so need to detect that.  Also improved error handling (show the detailed error if unable to create UploadResult object from response json.  
Tested on Mac: Firefox 21, Chrome 27, and Safari 6.  And Windows: IE 10 and Chrome 27.