set bit 11 in the file header (file names are UTF-8 encoded)

If bit 11 isn't set, the encoding is assumed to be IBM Code Page 437 (see http://www.pkware.com/documents/casestudies/APPNOTE.TXT), but the `fromString` function uses `encodeUtf8`. This becomes clear when you add an entry with special characters like 'ä' and then unpack the archive with something like `unzip`.

Technically, you'd also have to check this bit when reading an archive, but I don't know whether there even is a decoding function for IBM Code Page 437