Update list of browsers supporting filename* in Content-Disposition

When generating a download, we check the browser's user agent before writing the filename parameter of the Content-Disposition header. For some browsers, we use the filename field, while for the rest we use filename*. At the moment, Chrome supports filename*, but is grouped with Safari which we only set filename for. We should probably update the browser list in header_filename() to make sure that we are still sending down the correct field. RFC 6266 indicates that we can actually specify both parameters, so we might consider doing that.