Export does not work if german umlaute are in filename

[GoogleCodeExporter]

What steps will reproduce the problem?
1. create a button which onclicke does the export
2. set filename with äöü
3. download
4. http 404 ressource not found

What is the expected output? What do you see instead?
the download window to download the file

What version of the product are you using? On what operating system?
vaadin 7.1.9
table export 1.5.1.1

Please provide any additional information below.

src button:
        exportXLSButton.addClickListener(new ClickListener() {

            @Override
            public void buttonClick(com.vaadin.ui.Button.ClickEvent event)
            {
                ExcelExport excelExport = new ExcelExport(theTable, user.getDisplayName());
                excelExport.setExportFileName("sumary-Stephan-Grün"); //the ü is the problem
                excelExport.setExcelFormatOfProperty("count", "#");
                excelExport.setExcelFormatOfProperty("count1", "#");
                excelExport.setExcelFormatOfProperty("totalPrice", "#,##0.00 €");
                excelExport.setExcelFormatOfProperty("total", "#,##0.00 €");
                excelExport.excludeCollapsedColumns();
                excelExport.setReportTitle(user.getDisplayName());
                excelExport.export();

            }
        });

Original issue reported on code.google.com by christop...@gmail.com on 7 Apr 2014 at 8:22